GIFT   OF 
Bertha  Stut 


. 


OO"^ 


VTL^Crt 


MODERN    CHEMISTRY 


WITH    ITS    PRACTICAL 
APPLICATIONS 


BY 


FREDUS   N.    PETERS,   A.M. 

INSTRUCTOR  IN  CHEMISTRY  IN   CENTRAL  HIGH  SCHOOL, 

KANSAS  CITY,  MISSOURI 
AUTHOR  OF  "  EXPERIMENTAL  CHEMISTRY,"   ETC. 


NEW   YORK 

MAYNARD,   MERRILL,   &   CO. 
1905 


PY3 


COPYRIGHT,  1001,  BY 
MAYNARD,  MERRILL,  &  CO. 


6/ff 


PREFACE 

IN  preparing  this  book  for  use  in  secondary  schools,  I  have 
endeavored  to  look  at  the  science  from  the  viewpoint  of  the 
students  themselves.  The  fault  with  many  texts  upon  the 
same  subject  is  that  the  position  of  the  learner  has  been  disre- 
garded; the  books  have  been  encyclopaedic;  they  have  pre- 
sented a  great  number  of  facts  as  a  skeleton  or  framework, 
but  this  skeleton  has  not  been  clothed  with  muscle  and  ani- 
mated with  life.  No  more  fascinating  subject  finds  a  place 
in  the  curricula  of  our  secondary  schools,  yet  to  the  average 
student  chemistry  is  too  often  but  an  irksome  task. 

In  the  present  work  I  have  omitted  much  that  is  often 
given  in  an  elementary  text,  while  at  the  same  time  entering 
more  into  that  detail  which  gives  lively  interest  to  the  subject. 
It  has  been  my  aim  to  show,  whenever  possible,  the  practical 
application  of  the  science  to  the  everyday  affairs  of  life;  in 
other  words,  to  emphasize  industrial  and  commercial  chem- 
istry. At  the  same  time  the  fundamental  principles  of  the 
science  have  not  been  forgotten ;  on  the  contrary,  they  have 
been  emphasized  even  more  than  is  usual  in  an  elementary 
chemistry.  This  has  been  rendered  possible  by  the  omission 
of  much  that  can  never  be  either  of  interest  or  of  value  to  the 
beginner. 

Recognizing  the  fact  that  science  must  be  taught  inductively 
by  experiment,  some  authors  have  assumed  that  the  student 
must  gain  all  his  knowledge  of  chemistry  in  this  way.  No 
greater  mistake  could  be  made.  The  science  has  been  hun- 
dreds of  years  in  reaching  its  present  development,  and  much 
must  be  accepted  by  the  student  without  any  effort  to  work 
it  out  for  himself.  In  this  text  a  large  amount  of  experi- 

M  1832 


4  PREFACE 

mental  work  is  given,  sufficient  to  meet  the  requirements  of 
all  our  best  colleges.  The  experiment  is  always  supplemented 
by  notes  and  suggestions  which  enable  the  student  to  draw 
proper  conclusions,  and  give  him  such  information  as  he 
cannot  hope  in  his  limited  time  to  gain  for  himself.  It  will 
be  noticed  also  that  the  laboratory  directions  are  largely  in 
the  form  of  questions,  so  as  to  compel  even  the  least  ener- 
getic students  to  secure  the  benefits  of  personal  investigation. 
This  plan  is  always  followed  except  in  cases  where  the  student 
would  be  in  danger  of  going  astray. 

To  the  pedagogical  treatment  of  the  difficult  parts  of  the  sci- 
ence I  desire  to  call  attention.  The  subject  has  been  presented 
much  in  the  same  way  as  in  my  own  classes,  where  the  method 
has  met  with  success.  Beginning  with  the  study  of  that 
most  familiar  of  substances,  Water,  the  text  enters  into  a 
discussion  of  its  composition  and  then  proceeds  to  a  detailed 
statement  of  its  constituents.  This  work  is  prefaced  merely 
by  a  short  chapter  connecting  the  science  of  Chemistry  with 
that  of  Physics  and  by  one  chapter  upon  Valence.  This  some- 
what intricate  subject  of  Valence  was  introduced  early  by 
request  of  a  number  of  teachers,  to  avoid  many  difficult 
questions  that  must  arise  when  it  is  deferred.  Logically,  it 
would  come  later,  and  may  be  deferred  if  the  teacher  so 
desires.  However,  its  simple,  graphic  presentation  is  such 
that  the  student  can  hardly  fail  to  grasp  the  meaning. 

I  recognize  the  demands,  coming  from  all  higher  institutions 
of  learning,  for  more  quantitative  work,  and  believe  I  have 
fully  met  all  such  requirements.  The  student  of  the  subject, 
as  taught  hitherto,  has  been  in  danger  of  coming  to  the  con- 
clusion that  very  little  in  chemistry  is  exact ;  whereas  nothing 
could  be  further  from  the  truth.  The  pupil  is  shown  this 
by  the  series  of  quantitative  experiments  which  have  been 
carefully  worked  out  in  the  laboratory.  For  this  work  I  have 
sought  to  make  use  of  such  apparatus  only  as  may  be  or 
should  be  found  in  any  secondary  school. 


PREFACE  5 

To  the  regular  text  is  appended  detailed  instruction  for 
various  laboratory  manipulations,  preparing  solutions,  etc.  A 
chapter  has  also  been  added  for  the  benefit  of  any  who  may 
desire  to  continue  along  qualitative  lines  the  work  introduced 
at  various  places  in  the  text. 

I  desire  to  acknowledge,  with  gratitude,  the  valuable  sug- 
gestions offered  by  Professor  Irving  P.  Bishop,  of  the  State 
Normal  School,  Buffalo,  and  Professor  M.  D.  Sohon,  of  the 
Boys'  High  School,  New  York  City,  both  of  whom  have  read 
the  book  critically  in  manuscript ;  furthermore,  I  wish  to  say 
that  to  many  of  my  students  of  the  past  I  am  indebted  for 
descriptions,  original  with  them,  and  more  appropriate  than 
any  I  have  found  in  any  text.  To  Dr.  Paul  Schweitzer,  for 
many  years  Professor  of  Chemistry  in  the  Missouri  State  Uni- 
versity, the  true  friend  of  the  student,  to  whom  I  owe  much 
for  his  great  sympathy  and  encouragement,  and  his  words  of 
fatherly  advice,  I  desire  to  express  especial  gratitude.  Finally, 
I  acknowledge  with  pleasure  the  help  and  inspiration  I  have 
gained  in  my  private  study  and  research  from  the  writings  of 
those  who  have  been  permitted  to  drink  long  and  deep  from 
this  fountain  of  science. 


TO   THE   TEACHER 

IT  is  not  expected  that  everything  given  in  the  text  will  be 
demanded  of  the  pupil,  unless  possibly  in  reviews.  Some  of 
the  manufacturing  processes,  for  example,  I  have  deemed  of 
sufficient  importance  and  interest  to  be  given;  yet  it  may  seem 
best  in  the  judgment  of  the  instructor  to  omit  these. 

The  experiments,  as  a  rule,  may  be  performed  by  the  stu- 
dents, and  apparatus  is  suggested  which  most  schools  will  be 
able  to  provide.  The  number  of  pupils  will  determine  to 
some  extent  what  experiments  should  be  performed  by  the 
teacher  and  what  by  the  students  themselves.  If  the  classes 
are  small,  so  that  the  teacher  can  give  very  close  personal 
attention,  the  pupils  may  attempt  almost  all;  on  the  other 
hand,  if  the  classes  are  large,  it  may  be  necessary  for  the 
teacher  to  perform  some  of  the  more  difficult  and  dangerous  ex- 
periments himself.  On  pages  355  to  380  whi  be  found  many 
useful  suggestions  to  the  student  for  the  care  and  manipula- 
tion of  apparatus,  making  up  of  solutions,  etc.  These  should 
be  read  before  the  student  begins  his  work  in  the  laboratory, 
and  frequent  reference  should  afterward  be  made  to  them. 

It  is  presumed  that  a  school  year  of  nine  or 'ten  months  will 
be  given  to  the  work  in  this  text,  but  by  omitting  some  of  the 
less  important  elements,  much  of  the  theory  and  many  of  the 
practical  applications  of  chemical  science  may  be  obtained  in 
five  or  six  months.  Besides  the  various  chapters  devoted  to 
the  fundamental  laws  of  chemistry,  special  study  should  be 
given  to  the  following  elements  and  a  few  of  their  important 
compounds :  hydrogen,  oxygen,  nitrogen,  fluorine,  chlorine, 
bromine,  iodine,  carbon,  sulphur,  sodium,  calcium,  zinc,  lead, 
and  iron. 

6 


MODERN   CHEMISTRY 


CHAPTER    I 
INTRODUCTION       V. 


1.  With  what  is  Chemistry  concerned  ?  —  Nature  pre- 
sents herself  in  ever-changing  forms,  and  to  one  who  is 
not  familiar  with  these  variations  she  is  a  mystery.     The 
untaught  inhabitant  of  the  tropics,  who  has  never  been 
beyond  the  confines  of  his  native  state,  taken  to  a  colder 
climate  would  see  no  relation  between  the  snowflake  or 
the  icy  covering  of  our  northern  rivers  and  the  rain-drop 
as  it  falls  upon  his  native  hills.     To  him  they  are  entirely 
different  substances. 

2.  So  the  diamond,  the  filling  of  the  ordinary  "  lead " 
pencil,  and  the  coal  that  we  burn  in  our  furnaces  seem 
altogether  dissimilar,  and  yet  they  are  practically  the  same 
thing.      Likewise  the  emery  with  which  the  seamstress 
sharpens  her  needle  and  the  mechanic  his  tools,  and  such 
valuable  stones  as  the  oriental  emerald  and  the  ruby,  though 
seemingly  so  different,  have  really  the  same  composition. 
The  purpose  of  the  science  of  chemistry  is  the  investiga- 
tion of  the  objects  that  lie  all  about  us  in  nature,  the  study 
of  their  composition  and  of  their  relations  to  one  another, 
the  explanation  of  the  various  phenomena  in  connection 
with  them,  and  the  ability  to  apply  this  knowledge  to 
practical  uses. 

3.  Importance  of  the  Subject.  —  A  knowledge  of  chemis- 
try adds  a  charm  to  many  of  the  common  things  of  life, 

7 


8  MODERN   CHEMIST  UY 

clothing  them  with  new  beauty.  Later  it  will  be  noticed 
that  the  science  of  chemistry  enters  into  all  or  nearly  all 
of  the  great  manufacturing  industries  of  the  world,  and 
that  without  the  application  of  its  laws  and  principles  all 
such  enterprises  would  result  in  failure.  Whether  studied, 
tiiei'ef  ore,  '<f  pl-j  Jts  intellectual  or  for  its  practical  value,  it 
is'tof  the  greatest"  i'm^grtance. 

's'^  PHYSICAL  AND  CHEMICAL  CHANGES 


4.  Some  Theories  of  Matter.  —  There  have  been  men  in 
all  ages  who  believed  that  all  substances  whatsoever  might 
be  resolved  back  into  one  particular  kind  of  matter  ;  that 
by  subjecting  this  matter  to  different  conditions  an  end- 
less variety  of  modifications  would  result.     To  illustrate  : 
here  is  a  bar  of  steel  ;  by  submitting  it  to  varying  processes 
it  is  made  into  saws,  knives,  needles,  watch-springs,  pens, 
and  thousands  of  other  articles.     It  is  claimed  that  in  the 
same  manner  the  one  elementary  substance,  in  undergoing 
different  treatments  by  the  forces  of  nature,  appears  in 
the  endless  variety  of  substances  about  us.     It  has  never 
been  possible,  however,  for  those  who  hold  this  view  to 
prove  it  by  any  experiments.     Neither  does  it  seem  that 
the  phenomena  of  nature  require  or  even  admit  of  any 
such  explanation. 

5.  Elements.  —  What  seems    a    more  reasonable  view, 
and  one  that  has  come  nearer  to  demonstration,  is  that 
matter  is  composed  of  a  large  number  of  simple  substances, 
and  that  these   combined  in   different  ways  produce  an 
infinite  number  of  substances.     According  to  this  view 
there  are  about  seventy-five  simple  substances,  called  ele- 
ments,  which  cannot  be,   or   at   least   never    have    been, 
divided  into  two  or  more  simpler  substances.     Numerous 
experiments  of  every  character,  by  means  of  the  strongest 


ELEMENTS  9 

forces  known,  have  thus  far  failed  to  separate  these 
seventy-five  elements  into  anything  simpler.  If,  however, 
at  any  time,  we  should  by  some  method  succeed  In  thus 
decomposing  any  of  them,  they  would  no  longer  be 
regarded  as  elements.  The  following  is  a  list  of  the 
more  important:  — 

IMPORTANT  ELEMENTS* 


NAME 

Aluminum 
Antimony 

SYMBOL 

Al 
Sb 

As 

ATOMIC 
WEIGHT 

27 
120 
75 

ORDINARY 
VALENCE 

3 

3,5 
3,  5 

Ba 

137 

2 

Bismuth 

...        Bi 
B 

208 
11 

2 
3 

Br 

80 

1 

Cadmium 
Calcium 
Carbon  . 

Cd 

Ca 
.        .        C 

Cl 

112 

40 
12 
35.5 

2 
2 
4 
1 

Chromium 
Cobalt 

Cr 
Co 

52 
59 

3 

2 

Cu 

63 

2 

Fluorine 
Gold       . 
Hydrogen 
Iodine    . 

.        .        .         F 
Au 
H 
.        .        .        I 

.        .        .        .         Fe 

19 
197 
1 
127 
56 

1 
3 

1 
1 
2,  3 

Lead       . 

Pb 

207 

2 

Magnesium  -r 
Manganese     . 
Mercury 

Mg 
Mn 

•        •        •        •        Hg 

24 

55 
200 

2' 
2 

2 

*  Although  the  meaning  and  use  of  "symbols,"  "atomic  weight," 
and  "  ordinary  valence  "  have  not  yet  been  explained,  they  are  given  here 
for  future  reference.  The  weights  given  are  only  approximate,  the  deci- 
mals being  omitted.  For  a  more  complete  list  of  the  elements,  see  Ap- 
pendix E,  page  388. 


10 


MODERN  CHEMISTRY 


NAME 

Nickel    . 

Nitrogen 

Oxygen  . 

Phosphorus 

Platinum 

Potassium 

Silicon   . 

Silver     . 

Sodium  . 

Strontium 

Sulphur 

Tin 

Zinc 


IMPORTANT  ELEMENTS—  Continued 


SYMBOL 

Ni 

N 

O 

P 

Pt 

K 

Si 

Ag 

Na 

Sr 

S 

Sn 

Zn 


TOMIC 

HEIGHT 

ORDINABY 
VALENOB 

58 

2 

14 

3,5 

16 

2 

31 

3,5 

195 

4 

39 

1 

28 

4 

108 

1 

23 

1 

87 

2 

32 

2,4,6 

118 

2,4 

65 

2 

6.  Formerly  several  substances  were  classed  as  elements 
which  have  since  been  decomposed  by  electricity  and  found 
to  consist   of  two  or  three  simpler  substances.     In  the 
same  way,  it  is  not  improbable  that  some  of  the  rarer  sub- 
stances now  regarded  as  elements  may  sometime  in  the 
future  be  found  to  consist  of  two  or  more  of  the  common 

—elements  named  in  the  table  above. 

7.  Compound  Bodies.  —  A  compound  body  is  one  which 
consists  of  two  or  more  elements  chemically  united  in  a 
fixed  and  definite  proportion.     For  example,  if  I  put  a 
gram  of   common  cooking   soda   into  vinegar,  and   find 
that  five  cubic  centimeters  of  the  vinegar  are  necessary  to 
decompose,  or  dissolve,  the  soda,  then  in  every  instance 
five  parts  of  the  vinegar  will  be  needed  to  decompose  one 
part  of  the  soda.     That  is,  the  two  substances  always 
combine  with  each  other  in  the  same  ratio,  or  in  a  certain 
fixed  and  definite  proportion,  and  the  substance  resulting 
from  the  combination  always  bears  a  certain  ratio  to  each 
of  the  others.    Thus,  common  salt  is  a  compound  body,  con- 


MOLECULES  AND  ATOMS  ll 

sisting  of  two  elements,  sodium  and  chlorine,  always  in  the 
ratio  of  46  to  71  by  weight.  Likewise,  water  is  a  com- 
pound, containing  one  part  of  hydrogen  to  eight  of  oxygen. 
8.  Divisibility  of  Matter. — Physics  teaches  us  that 
matter  is  anything  that  occupies  space,  and  that  all  matter 
is  divisible.  But  where  does  this  divisibility  end?  We 
do  not  know.  A  single  crystal  of  a  dark  purple  solid 
known  as  potassium  permanganate  will  very  perceptibly 
color  several  gallons  of  water.  To  do  this,  it  must  be 
divided  up  until  its  particles  are  diffused  throughout  the 
entire  volume  of  the  water,  or  into  so  many  parts  that 
the  numbers  are  beyond  our  comprehension.  Though  we 
cannot  fix  an  absolute  limit  to  the  division  of  matter,  we 
assume  it  to  be  the  molecule. 

SJ-  The  Theory  of  Molecules.  —  A  molecule  is  the  smallest 
particle  of  matter  that  can  exist  alone,  or  in  the  case  of  a 
compound  body,  the  smallest  particle  that  can  exist  with- 
out destroying  the  identity  of  the  substance.  Thus,  the 
smallest  portion  of  common  salt  to  be  conceived  of  still 
contains  the  two  elements  mentioned,  sodium  and  chlorine, 
and  is  a  molecule.  In  the  same  way  the  smallest  particle 
of  water  would  contain  both  hydrogen  and  oxygen,  and 
always  in  the  same  ratio.  If,  now,  by  any  means  we  can 
break  up  these  salt  or  water  molecules  into  their  two  con- 
stituents, we  no  longer  have  a  compound  body,  but  two 
simpler  substances  or  elements. 

"HO.  Atoms.  —  These  constituent  parts  of  a  molecule  we 
call  atoms.  Even  the  molecules  of  the  elements  may  con- 
sist of  two  or  more  atoms ;  in  fact,  they  usually  do. 
Thus,  it  will  be  seen  later  that  a  molecule  of  oxygen  con- 
sists of  two  atoms ;  a  molecule  of  chlorine  of  two  atoms, 
and  so  on.  It  may  be  said,  therefore,  that  all  matter  is 
divisible  into  molecules,  and  that  these  molecules  are 


12 


MODEEN  CHEMISTRY 


composed  of  still  smaller  particles  called  atoms.  From 
the  above,  it  will  be  seen  that  the  molecule  of  the  com- 
pound body  and  its  constituent  atoms  would  be  very  dif- 
ferent, while  the  molecule  of  an  elementary  body  and  its 
atoms  would  be  exactly  alike  in  properties.  This  is  illus- 
trated in  Fig.  1. 

Here,  a  represents  a  molecule  of  water  consisting  of  two  atoms  of 
hydrogen  and  one  of  oxygen.  If  by  electricity  we  decompose  this 
molecule,  we  shall  no  longer  have  water,  but 
two  elementary  substances,  hydrogen  and  oxy- 
gen. Likewise,  c  represents  a  molecule  of 
common  salt,  and  if  this  be  decomposed,  we 
shall  no  longer  have  salt,  but  two  substances, 
sodium  and  chlorine.  On  the  other  hand,  b 
represents  a  molecule  of  oxygen,  and  if  this 
be  decomposed,  we  shall  still  have  oxygen, 
but  in  the  atomic  form,  possessing  the  same 
physical  characteristics  as  before. 

\11.  Physical  Changes. — Matter  exists  in  three  condi- 
tions, solid,  liquid,  and  gaseous,  depending  upon  the  rela- 
tion to  each  other  of  the  intermolecular  forces.  When 
the  cohesion  existing  between  the  molecules  is  consider- 
ably greater  than  the  repellant  forces  which  tend  to  drive 
them  apart,  the  substance  exists  in  the  form  of  a  solid. 
When  the  converse  of  this  is  true,  and  the  molecules  tend 
to  be  driven  farther  and  farther  from  each  other,  the  sub- 
stance is  then  in  the  form  of  a  gas.  When  the  repellant 
and  attractive  forces  are  about  at  an  equilibrium,  the 
substance  exists  as  a  liquid.  It  is  with  changes  of  molec- 
ular condition  that  physics  deals,  and  the  molecule  is  the 
basis  of  all  physical  phenomena. 

EXPERIMENT  1.  —  Hold  in  the  flame  of  the  Bunsen  burner  a  piece 
of  tin  foil,  an  aluminum  wire,  or  a  narrow  strip  of  zinc;  or  put  any 
one  of  them  into  a  clean  iron  spoon  and  heat.  What  change  takes 


PHYSICAL   CHANGES  13 

place  in  the  physical  condition  of  the  metal?    Let  it  cool  again  and 
state  what  happens. 

12.  In  this  simple  experiment  two  changes  have  taken 
place :    one,  the  conversion  of   the  solid  into  the  liquid 
form ;  and  second,  the  changing  back  again  into  the  solid. 
We   have  changed   the  form  of   the  substance  and  the 
arrangement  of  the  molecules  as  regards  one  another,  but 
the  properties  have  remained  the  same. 

13.  Another  Molecular  Change.  —  Likewise,  when  a  cur- 
rent of  electricity  is  passed  through  an  electro-magnet, 
the  armature  for  the  time  being  becomes  a  magnet ;  that 
is,  its  molecules  have  been  rearranged,  or  so  affected  that 
they  present  the  well-known  phenomenon  of  attraction. 
When  the  circuit  is  broken,  the  armature  loses  its  mag- 
netism ;  in  other  words,  its  molecules  have  assumed  their 
previous  condition.     When  a  body  is  heated,  the  molecules 
are  set  in  more  rapid  vibration,  and  luminous  bodies  emit 
light  because  of  this  vibratory  motion. 

14.  So  throughout  the  domain  of  physics  we  find  that 
all  phenomena  concern  the  molecule  and  molecular  changes. 
We  are  all  familiar  with  the  different  conditions  under 
which  water  exists,  and  we  are  not  surprised  at  the  state- 
ment   that   fog,  clouds,  rain,  snow,  and  other  forms  are 
modifications  of  the  same  substance,  the  only  difference 
being  in  the  greater  or  less  amount  of  stored-up  heat 
energy. 

15.  Substances  exist  in  Three  Forms.  —  At  the  same  time 
we  are  not  accustomed  to  think  that  nearly  all  substances 
may  exist  in  the  same  three  forms ;  as  liquids,  solids,  and 
gases.     We  are  familiar  with  air  in  the  gaseous  condi- 
tion only ;  yet  if  we  reduce  the  temperature  of  it  to  about 
190°    below    zero  Centigrade,  it   becomes   a   transparent 
liquid  not  very  different  in  appearance  from  water,  and 


14  MODERN  CHEMISTRY 

at  a  still  lower  temperature  it  freezes  or  solidifies.  In 
like  manner  carbon  dioxide,  an  invisible  gas  thrown  off 
from  the  lungs  of  all  animals  in  breathing,  if  cooled,  is 
first  liquefied,  and  then  by  further  reduction  of  tempera- 
ture is  converted  into  a  beautiful  white  crystalline  solid, 
very  closely  resembling  snow. 

16.  Mercury  and  Carbon.  —  We  are  all   familiar  with 
mercury  as  a  silvery  white  liquid,  which  may  be  boiled 
and  converted  into  vapor  at  a  moderately  low  temperature. 
On  the  other  hand,  in  our  most  northern  climates  it  fre- 
quently solidifies,  and  were  the  glacial  epoch  to  return, 
under  the  rigors  of   that  era  we  would  know  mercury, 
not  as  a  liquid,  but  as  a  somewhat  malleable  solid  closely 
resembling  lead  in  its  appearance  and  properties.     To  go 
still  further,  carbon,  that  we  know  best  in  the  form  of 
charcoal  and  coal,  —  one  of  the  most  refractory  of  sub- 
stances—  in  an  electrical  furnace  may  be  fused  and  made 
to  drip  from  the  ends  of  the  carbon  electrodes,  while  in 
the  intense  heat  of  the  sun,  it  is  thought  to  exist  in  the 
atmosphere  surrounding  that    body  just  as  water  vapor 
does  in  our  own. 

17.  All   these  are  merely  illustrations  of   changes   in 
molecular   condition,  or   are  physical   changes;    and   the 
same  substance  in  its  different  forms  presents  at  all  times 
essentially  the  same  properties. 

EXPERIMENT  2.  —  Put  into  a  small  test-tube  a  crystal  of  iodine 
and  warm  gently.  What  -becomes  of  the  crystal?  Does  anything 
deposit  farther  up  the  tube?  When  the  colored  vapors  have  disap- 
peared, warm  the  tube  higher  up.  What  happens? 

From  the  above  experiment  we  see  what  has  been  stated 
before,  that  heat  converts  many  substances  into  vapors ; 
and  further,  that  when  this  heat  is  removed,  they  condense 
again  into  their  previous  condition.  We  learn,  too,  that 


CHEMICAL   CHANGES  15 

the  physical  condition  in  which  bodies  exist  is  not  an  essen- 
tial, but  an  incidental  matter  depending  upon  the  ease  or 
difficulty  with  which  they  are  melted  and  vaporized. 
\18.  Chemical  Changes.  —  Chemical  changes,  on  the  other 
hand,  involve,  not  the  molecule,  but  the  constituent  parts 
of  the  molecule,  the  atoms.  In  every  chemical  change  the 
molecule  is  broken  up  and  its  identity  destroyed,  while 
the  atoms  formerly  composing  it  recombine  to  form  new 
and  different  substances.  Hence,  when  any  substance  is 
changed  chemically,  or  when  two  or  more  substances  react 
upon  one  another  and  undergo  a  chemical  change,  new 
products  are  formed,  differing  altogether  in  properties 
from  the  original  substances. 

EXPERIMENT  3.  —  Put  into  a  small  test-tube  a  little  mercuric  oxide 
and  heat,  gently  at  first,  then  quite  strongly.  Continue  this  for  sev- 
eral minutes.  Thrust  a  pine  splinter,  having  a  spark  upon  the  end, 
down  into  the  tube.  What  happens  ?  Is  there  any  evidence  of  some- 
thing present  different  from  air?  What  seems  to  be  forming  upon 
the  cooler  portions  of  the  tube  ? 

19.  If  we  continue  to  heat  long  enough,  the  red  oxide 
would  entirely  disappear,  just  as  water  does  when  boiled. 
In  the  latter  case,  however,  the  water  might  be  condensed 
again  as  before,  while  in  the  present  instance  the  mercuric 
oxide  seems  to  be  decomposed  into  two  substances,  —  one, 
an  invisible  gas  which  caused  the  spark  to  burn  brightly, 
the  other  a  dark  colored  substance  which  condensed  in 
small  globules  upon  the  cooler  portion  of  the  tube.     Here 
we  have  a  chemical  change,  one  which  caused  the  destruc- 
tion of  the  original  substance,  and  produced  therefrom 
two,  differing  very  strikingly  in  their  properties. 

20.  Chemical  changes  are  usually  brought  about  by  some 
physical  agency,  such  as  heat,  electricit}r,  light,  percussion, 
etc.     Innumerable  instances  of  this  kind  of  change  might 


16  MODERN  CHEMISTRY 

be  given,  but  as. such  changes  are  to  be  studied  throughout 
the  science  of  chemistry,  only  a  few  will  be  noticed  at 
present.  As  already  seen,  the  substances  produced  are 
often  very  different  from  those  used  in  obtaining  them ; 
for  example,  two  or  more  solids  may  unite  in  such  a  way 
as  to  form  a  gaseous  body,  or  even  a  liquid ;  two  gases 
may  form  a  solid  or  a  liquid;  while  two  liquids  may 
combine  to  form  a  solid.  Some  of  these  will  be  illus- 
trated below. 

EXPERIMENT  4.  —  Rub  vigorously  together  in  a  mortar  a  small 
crystal  of  potassium  chlorate  and  an  equal  quantity  of  flowers  of 
sulphur.  Into  what  are  the  two  solids  converted?  How  is  their 
chemical  union  manifest? 

21.  A  change  similar  to  this  is  seen  when  gunpowder 
is  exploded,  causing  the  three  substances,  of  which  it  is 
a  mixture,  to  combine,  with  the  formation  of  several 
gaseous  products. 

EXPERIMENT  5.  —  With  a  few  small  crystals  of  potassium  chlorate 
wrap  in  a  piece  of  paper  a  bit  of  phosphorus ;  fold  the  ends  together 
carefully  and  strike  with  a  heavy  weight  as  shown  in 
Fig.  2.    What  are  the  results?    What  is  the  nature  of 
the  products  formed? 

CAUTION.  —  In  preparing  for  this  experi- 
ment, cut  the  phosphorus  under  water,  dry 
quickly  in  the  folds  of  a  filter  or  blotting 
paper,  and  proceed  as  above.  Small  parti- 
cles of  the  phosphorus  often  fly  to  some  dis- 
tance, and  a  board  should  be  set  up  to  protect 

the  clothing  of  the  experimenter  and  of  the  members  of 

the  class. 

EXPERIMENT  6.  —  Mix  thoroughly  a  small  quantity  of  'granulated 
sugar  with  an  equal  amount  of  potassium  chlorate,  well  powdered, 
and  put  the  mixture  into  an  iron  saucer.  Now  by  means  of  a  pipette 


CHEMICAL   CHANGES 


17 


or  glass  tube  drop  upon  it  a  little  strong  sulphuric  acid.  Notice  that 
the  sugar  is  burned,  a  part  is  converted  into  gaseous  products,  and  a 
part  left  as  a  black  residue. 

J22.  Chemical  Change  by  Physical  Agency.  —  In  Experi- 
ments 3,  4,  and  5,  the  different  substances  were  caused  to 
combine  by  friction,  or  percussion.  That  is,  by  physi- 
cal force,  the  molecules  of  the  different  substances  were 
brought  so  close  together  that  the  chemism,  or  chemical 
affinity,  of  the  atoms  in  the  unlike  substances  was  greater 
than  the  cohesion  among  the  molecules,  and  as  a  result 
the  atoms  rearranged  themselves  to  form  new  compounds. 
This  may  also  be  illustrated  by  the  following  experiment : 

EXPERIMENT  7.  —  Put  into  a  clean  porcelain  mortar  a  few  crystals 
of  potassium  iodide,  KI,  and  about  the  same  amount  of  mercuric 
chloride,  HgClr  Rub  them  together  for  two  or  three  minutes;  notice 
that  the  two  white  compounds  react  with  each  other  to  form  a  bright 
red  mixture. 


23.  By  the  friction,  the  molecules  of  the  mercuric  chlo- 
ride and  of  potassium  iodide  are  brought  so  close  together, 
that  the  mercury  and  potassium  atoms  exchange  places, 
forming  mercuric  iodide,  which  is  bright  red  in  color,  and 
potassium  chloride,  which  is  a  white  compound.  It  is 
simply  another  striking  illustration  of  the  fact  already 
stated  that  chemical  action  brings  about  a  change  in  the 
atomic  structure,  and  causes,  therefore,  the  formation  of 
substances  very  different  from  the  original. 


18  MODERN  CHEMISTRY 

24.  Chemical  Change  by  Chemical  Agent.  —  In  Experi- 
ment 6,  the  same  results  were  brought  about  by  the  use 
of  a  chemical  reagent,  sulphuric  acid.  In  all  of  these 
instances,  except  Experiment  7,  the  solid  substances  used 
were  largely  converted  into  gaseous  products,  and  in  all 
entirely  different  from  the  original.  To  show  that  two 
gases  may  combine  to  form  a  solid,  perform  the  following 
experiment :  — 

EXPERIMENT  8.  —  Put  into  a  beaker  a  few  drops  of  hydrochloric 
acid,  cover  with  a  sheet  of  cardboard  or  glass,  and  allow  it  to  stand  a 
few  minutes.  Into  another  beaker  put  a  few  drops  of  strong  ammo- 
nium hydroxide,  and  cover  in  the  same  way.  Presently,  invert  the 
first  beaker  over  the  second,  then  remove  the  cards,  so  that  the  two 
gases  which  have  filled  the  beakers  may  come  into  contact  with  each 
other.  Notice  the  heavy  white  fumes  that  form.  These  are  a  white 
solid  compound,  known  as  sal  ammoniac. 

EXPERIMENT  9.  —  To  show  that  two  liquids  by  reacting  upon  each 
other  may  produce  a  solid.  Numerous  instances  of  this  will  be  seen 
from  time  to  time.  Powder  a  gram  or  two  of  alum  and  an  equal 
amount  of  ferrous  sulphate,  put  both  into  a  test-tube  and  add  about 
lOcc.  of  water  or  just  enough  to  dissolve  them  readily.  You  will  now 
have  a  nearly  colorless  solution.  To  this  add  slowly  a  little  strong 
ammonium  hydroxide.  You  will  obtain  a  greenish  colored,  jelly-like 
solid,  with  scarcely  enough  water  present  to  enable  the  precipitates  to 
be  poured  from  the  tube. 

x  25.  Mixtures.  — We  have  had  the  term  compound  body 
defined,  and  we  must  be  careful  to  distinguish  between  a 
compound  and  a  mixture.  In  the  latter,  the  two  or  more 
substances  used  are  not  necessarily  in  any  definite  propor- 
tion, nor  are  they  united  with  each  other.  Furthermore, 
as  a  rule,  mixtures  may  be  very  easily  separated  by  purely 
mechanical  means. 

Thus,  we  may  put  together  sand  and  common  salt  in 
any  proportion  whatsoever ;  they  do  not  react  with  each 
other  to  form  a  new  compound,  but  are  still  sand  and  salt 


MIXTURES  19 

just  as  before  being  mixed.  They  may  also  be  very  easily 
separated  and  the  salt  recovered.  Let  the  student  suggest 
a  method  for  doing  this. 

[26.  Gunpowder.  —  Gunpowder  is  a  very  familiar  mix- 
ture, consisting  of  three  substances  which  may  be  easily 
separated.  Upon  exploding,  however,  these  three  combine 
to  form  several  compounds  from  which  the  original  could 
be  recovered  only  by  difficult  and  expensive  methods. 

EXPERIMENT  10.  —  To  separate  gunpowder  into  its  constituents. 
Put  a  gram  or  two  of  gunpowder  into  an  evaporating  dish  and  add  a 
few  cubic  centimeters  of  water.  After  warming  gently  a  few  minutes, 
filter  out  as  directed  on  page  364.  Transfer  the  clear  filtrate  to  an 
evaporating  dish  and  boil  slowly  to  dry  ness.  While  you  are  waiting 
for  this,  transfer  the  black  residue  upon  the  filter  paper  to  a  beaker 
and  add  a  little  carbon  disulphide.  Shake  for  a  moment  or  two,  and 
then  decant  or  filter  off  this  clear  solution.  Without  heating,  let  it 
evaporate  to  dryness  in  a  watch  crystal  or  evaporating  dish.  What 
familiar  substance  is  left?  What  was  the  appearance  of  the  solid 
obtained  by  boiling  down  the  solution  in  water?  What  colored  resi- 
due was  left  after  treating  with  carbon  disulphide?  Can  you  name 
the  three  substances? 

EXPERIMENT  11.  —  To  show  the  difference  between  a  mixture  and 
a  compound  of  the  same  two  elements.  Put  together  in  any  proportion 
a  small  quantity  of  sulphur  and  of  iron  filings.  Mix  them  thoroughly. 
What  is  the  resulting  color?  See  whether  you  can  remove  the  filings 
by  means  of  a  magnet ;  owing  to  the  presence  of  some  moisture  a 
little  sulphur  may  adhere  to  the  filings.  State  your  results.  Put  the 
filings  back  into  the  sulphur  and  again  mix  them  well.  Now  add 
1  or  2  cc.  of  carbon  disulphide,  shake  for  a  moment  or  two,  and 
decant  thoroughly  upon  a  watch  crystal  or  into  an  evaporating  dish. 
Let  the  clear  solution  dry  without  heating,  as  it  is  very  inflammable. 
What  do  you  obtain  ?  Have  you  effected  a  separation  of  the  two  ? 

Again  mix  in  about  equal  proportions  by  volume,  or  in  the  ratio 
of  32  to  56  by  weight,  sulphur  and  iron  filings ;  put  them  into  the 
smallest  test-tube  you  have  and  heat,  first  gently  and  then  very 
strongly,  until  a  bright  red  glow  seems  to  go  through  the  entire  mass. 
After  thus  heating  for  two  or  three  minutes,  allow  the  tube  to  cool, 


20  MODERN  CHEMISTRY 

and  remove  the  contents ;  if  necessary,  break  the  tube.  How  does 
the  color  differ  from  that  of  the  mixture  at  the  beginning?  Powder 
the  mass,  and  attempt  to  separate  the  filings  from  the  sulphur  by 
means  of  a  magnet  as  before.  Can  you  do  this?  Treat  a  part  of 
the  dark  powdered  mass  with  carbon  disulphide  and  determine 
whether  you  can  thus  remove  the  sulphur  as  you  did  from  the  mix- 
ture. State  your  results.  From  this  experiment  we  may  note  several 
differences  between  the  mixture  of  iron  and  sulphur  that  we  had 
before  heating  and  the  compound  afterward.  What  are  they? 


SUMMARY  OF   CHAPTER 

Introduction. 

Some  theories  of  matter  —  Old  —  Illustration. 

Present  theory. 

Definition  of  term  element. 
Compound  bodies. 

Definition. 

Illustration. 
Divisibility  of  matter.  Chemical  changes. 

Difference  between  molecule          How  different  from  physical, 
and  atom.  Several  experiments  to  illustrate. 

Illustration.  Mixtures. 

Physical  changes.  How  different  from  elements  and 

Experiments  to  illustrate.  compounds. 

Name  several  others.  Examples  of  mixtures. 

What  is  a  physical  change?          Method  of  separating. 


CHAPTER  II 

VALENCE 

x'  1.  What  is  Valence  ?  *  —  If  we  notice  some  of  the  com- 
mon compounds  of  hydrogen,  which  we  shall  study,  we 
shall  see  that  different  elements  unite  with  a  different 
number  of  hydrogen  atoms.  Thus,  chlorine  combines  with 
one  atom  of  hydrogen,  oxygen  with  two,  nitrogen  with 
three,  and  carbon  with  four,  as  shown  in  the  following 
compounds :  — 

Hydrochloric  Acid  ....     HC1 
Water H2O 

Ammonia  .  H«N 

o 

Marsh  Gas H4C 

2.  The  four  elements,  chlorine,  oxygen,  nitrogen,  and 
carbon,  have  the  power  of  combining  with  one,  two,  three, 
and  four  atoms  of  hydrogen,  respectively,  and  we  speak 
of  them  as  having  a  valence  of  one,  two,  three,  and  four. 
By  valence  or  quanti valence  we 
mean  the  power  any  element  has  0  ,  , 

of     holding    in    combination    the    N> • • 1 

j  atoms   of   another   element   taken 
as  a  standard.     This  standard,  primarily,  as  shown  above, 

*  If  in  the  judgment  of  the  teacher  the  subject  of  valence  can  be  more 
easily  grasped  by  the  student  later  in  the  course,  this  chapter  may  be 
deferred  until  after  the  study  of  carbon  and  its  compounds. 

21 


22  MODERN  CHEMISTRY 

is  hydrogen,  and  by  it  the  valence  of  other  elements  is 
measured  or  determined.  It  may  be  illustrated  in  this 
way:  suppose  the  first  line  represents  the  combining 
power  of  hydrogen,  which  is  our  standard.  Then  with 
this  "  yard  stick  "  we  will  measure  the  combining  power 
of  the  other  elements.  In  water,  H2O,  the  valence  of 
the  oxygen  atom  is  determined  by  applying  the  "yard 
stick,"  and  is  seen  to  be  two  ;  in  NH3  the  standard  is  used 
three  times,  and  the  valence  of  the  nitrogen  atom  is  three. 
In  the  same  manner  the  valence  of  the  carbon  atom  is 
determined  as  four. 

3.  Suppose,  however,  hydrogen  did  not  combine  with 
carbon,  could  we  still  determine  its  valence  ?  We  are 
familiar  with  the  compound,  carbon  dioxide.  In  this 
molecule,  CO2,  the  oxygen  atom  is  used  twice  with  the 
carbon  atom,  hence  the  latter  must  have  twice  the  combin- 
ing power  of  the  oxygen.  This  has  already  been  shown 
to  be  two,  hence  carbon  would  be  four. 

To  illustrate  roughly,  we  sometimes  speak  of  the  atoms 
as  having  a  certain  number  of  "bonds"  or  "poles  of 
attraction,"  represented  as  below  :  — 

@p     Atoms  with  one  "  bond." 
Atoms  with  two  "  bonds." 
Atoms  with  three  "bonds." 
Atoms  with  four  "bonds." 


From  this  illustration  it  will  be  seen  that  an  atom  in 
the  second  group  in  combining  would  have  two  bonds  by 


VALENCE 


23 


which  to  hold  the  two  bonds  of  two  individual  atoms  of 
the  first. 


Mercuric  Bromide. 


Water. 


N  and  Sb  both  have  valence 
(&)  (ri^  of  three. 

Ammonia.        Antimony  Chloride. 


C  and  Si,  valence  of  four. 


Silicon  Dioxide. 


4.  Such  atoms  as  combine  with  one  of  hydrogen  or  its 
equivalent  are  said  to  be  univalent,  or  are  sometimes  called 
monads;  those  which  combine  with  two  of  hydrogen  are 
bivalent,  or  dyads;  with  three,  trivalent,  or  triads ;  with 
four,  quadrivalent,  or  tetrads;  with  five,  quinquivalent,  or 
pentads. 

5.  Variation  in  Valence.  —  In  studying  a  number  of  the 
compounds  of  any  element  it  will  be  noticed  that  while 
the  valence  of  the  element  in  most  of  them  is  the  same, 
there  will  be  some  compounds  which  show  it  to  be  dif- 
ferent.    Many  of  these  are  believed  to  be  merely  apparent 
exceptions  and  may  be  readily  explained ;  while  others, 
as  yet  not  thoroughly  understood,  may  be  real  variations. 
For  example,  the  oxygen  atom  is  always  regarded  as  biva- 
lent, yet  we  shall   meet  with  the  compound,  hydrogen 
peroxide,  H2O3,  in  which  oxygen  is  apparently  univalent. 


24  MODERN  CHEMISTRY 

It  is  believed,  however,  that  the  atoms  have  an  arrange- 
ment in  the  molecule  which  may  be  represented  thus  :  — 


or 


This  simply  means  that  one  bond  of  each  atom  of 
oxygen  is  held  by  a  bond  of  the  other.  In  a  similar  way 
the  apparent  double  valence  of  a  great  many  other  ele- 
ments is  explained.  Thus  copper  and  mercury,  ordinarily 
bivalent,  also  form  the  compounds  Cu2Cl2,  and  Hg2Cl2. 
But  these  are  exactly  parallel  to  the  case  above. 


Bivalent.  Apparently  Bivalent.  Apparently 

Univalent.  Univalent. 

6.  Again  we  shall  study  the  two  compounds  of  carbon, 
CO  and  CO2,  the  first  of  which  would  indicate  a  valence 
of  two  for  the  atom,  while  in  the  second  it  would  be  four. 
The  second  is  believed  to  show  the  true  valence,  and 
carbon  monoxide  is  regarded  as  an  unsaturated  compound, 
that  is,  one  in  which  the  valence  of  the  atom  is  not  satisfied, 
or  one  in  which  a  part  of  the  bonds  is  not  held  by  any 
other  element.  We  may  represent  it  thus  :  — 


Saturated  Unsaturated 

Compound.  Compound. 

This  theory  is  accepted  because  carbon  monoxide  very 
readily  takes  up  one  more  atom  of  oxygen  and  forms  the 
dioxide. 


VALENCE  25 

7.  Double  Valence.  —  In  the  examples  of  double  valence, 
noticed  above,  the  irregularity  is  only  apparent.    There  are 
many  cases,  however,  in  which  all  the  indications  thus  far 
would  show  that   the  valence  of   the  atom  is  variable. 
Thus  we  have  said  the  nitrogen  atom  is  trivalent,  and 
this  is  so  in  ammonia  and  nitrogen  trioxide ;  but  we  shall 
also  meet  with  nitrogen  pentoxide,  N2O5,  in  which  the 
valence  is  five  ;  the  monoxide,  N2O,  wherein  it  is  appar- 
ently one,  etc.     There  are  many  such  variations  that  will 
trouble  the  student,  but  for  our  present  work  we  shall 
need,  as  a  rule,  to  aid  us  in  writing  formulae  and  reactions, 
only  a  knowledge  of  the  ordinary  valence  of  the  atoms. 

8.  Valence  of  Groups  or  Radicals.  —  We  shall  find  also 
that  many  groups  of  atoms  react   in  the   game  way  as 
individual  atoms  ;  such  groups  are  called  radicals.     They 
have  combining  power  or  valence  just  as  individual  atoms 
have.    Thus  when  sulphuric  acid  reacts  with  zinc,  we  shall 
find  that  the  group  (SO4)  is  not  broken  up ;  the  same  is 
true  in  hundreds  of  other  instances.     As  it  is  combined 
with  two  atoms  of  hydrogen  in  H2SO4,  and  always  does 
combine  in  the  same  way,  we  say  its  valence  is  two ;  this 
may  be  shown  graphically  in  this  way. 


(SO4)    Group,    showing  Sulphuric  Acid,  showing  all  bonds 

two  bonds  unused.  of  the  (SO4)  group  saturated. 

While  we  cannot  prove  that  such  is  the  arrangement  of 
the  atoms  in  the  group,  still  it  is  believed  to  be  true ;  at 
any  rate  it  serves  to  illustrate  how  the  valence  of  the 
group  is  two.  In  the  same  way  we  would  show  the 
valence  of  any  other  radical.  In  sal  ammoniac,  NH^Cl,  we 


26  MODERN  CHEMISTRY 

find  the  group  (NH4)  in  combination  with  one  atom  of 
chlorine,  hence  its  valence  is  one.  Then  if  the  radical 
(NH4)  combines  with  (SO4),  it  must  be  used  in  the 
proportion  of  two  of  the  former  to  one  of  the  latter,  thus 
(NH4)2S04. 


Cl] 


Sulphuric  Acid.  Ammonium  Ammonium 

Sulphate. 

Or  we  may  show  the  same  facts  in  this  way  :  — 


Ammonium,  showing  Ammonium  Sulphate,  showing  how  (SO4) 

one  bond  unused.  can  unite  with  two  of  (NH4). 

Exercise  in  Valence.*  —  Applying  the  principles  set  forth  in  the  pre- 
ceding paragraphs,  let  the  student  write  the  formulae  for  the  fol- 
lowing :  — 

when  Ba  unites  with  I,  Cl,  Br,  O,  NO3,  Cr04. 

when  Na  unites  with  O,  S,  Cl,  CIO,,  SiO4,  SO4. 

when  Cu  unites  with  Cl,  S,  SO4,  IIO,  O,  I. 

when  NH4  unites  with  T,  PO4,  SO4,  S,  HO,  Br. 

when  Bi  unites  with  Cl,  O,  S,  NO3,  SO4. 

*  Let  the  teacher  give  further  exercises  until  the  student  can  write  with 
assurance  the  compound  resulting  from  the  union  of  any  two  of  these 
elements  or  radicals. 


VALENCE  27 


The  valence  of  each  of  the  above  and  certain  others 

is  shown 

below  :  — 

MONADS 

MONADS 

DYADS 

DYADS 

TRIADS 

TKTEADS 

I 

Li 

Ba 

Cu 

Sb 

C 

Br 

(NH4) 

Zn 

Fe 

Bi 

Si 

Cl 

(NOS) 

Ca 

S 

As 

(SiOJ 

F 

(CIO,) 

Sr 

(S04) 

(PO^ 

Na 

(HO) 

O 

(Cr04) 

K 

Hg 

lonization.  —  Closely  related  to  the  idea  of  valence 
is  that  of  ionization.  Attempts  to  pass  a  current  of  elec- 
tricity through  a  vessel  of  pure  water  meet  with  very 
indifferent  success.  Again,  if  the  electrodes  of  a  battery 
be  placed  in  a  cup  of  dry  salt,  no  current  is  transmitted; 
however,  if  a  little  of  the  salt  be  dissolved  in  the  pure 
water,  the  solution  becomes  a  good  conductor. 

10.  Explanation.  —  It   is   well   known   to   students   of 
physics  that  water  containing  a  solid  in  solution  boils  at 
a  higher  temperature  than   pure  water.      For  example, 
water  saturated  with  common  salt  boils  at  108°  C. ;  with 
potassium    nitrate,    116°;    with    calcium   chloride,   179°. 
Numerous  experiments  have  shown  that  this  rise  of  boil- 
ing point  is  proportional  to  the  amount  of  the  substance 
dissolved ;   furthermore,  to  secure  a  like  change  in  the 
lowering  of  the  vapor  tension  when  different  substances 
are  dissolved,  it  is  found  that  amounts  proportional  to  the 
molecular  weights  of  the  substances  must  be  used.     (See 
page  68.)     To  illustrate,  suppose  the  molecular  weight  of 
the  compound  A  is  342  and  of  B  46,  then  to  secure  like 
results  in  lowering  of  vapor  tension,  we  should  be  required 
to  dissolve  portions  of  the  salts  in  the  ratio  of  342  to  46. 

11.  Exceptions.  —  When,   however,   we    dissolve    such 
substances  as  common  salt,  NaCl,  we  find  a  lowering  of 
the  vapor  tension  about  double  what  we  should  expect, 


28  MODERN  CHEMISTRY 

and  with  calcium  chloride,  CaCl2,  about  three  times. 
Furthermore,  such  solutions  are  good  conductors  of  elec- 
tricity, while  the  others  are  not. 

12.  Conclusion.  —  Putting  all  the  facts  together,  we  are 
led  to  believe  that  those  substances  which  lower  the  vapor 
tension  abnormally,  when  dissolved  in  water,  are  broken 
up  into  parts  or  ions.     Thus,  common  salt  becomes  largely 
ionized  into  sodium  and  chlorine  ions,  and  calcium  chlo- 
ride into  calcium  and  chlorine  ions,  etc. 

13.  Negative  and  Positive  Ions.  —  If  a  V-shaped  tube 
is  filled  with  a  dilute  solution  of  common  salt  and  a  cur- 
rent of  electricity  passed  through  it,  the  sodium  ions  will 
tend  to  collect  at  one  electrode  and  the  chlorine  at  the 
other.     This  may  be  proved  by  adding  a  few  drops  of  a 
solution  of  phenolphthalein.     It  will  be  found  that  the 
sodium   ions  collect   at   the  negative  electrode  and   the 
chlorine  at  the  positive.     From  the  well-known  law  of 
electrical  attraction,  we  know,  therefore,  that  the  sodium 
ions  are  positive  and  the  chlorine  are  negative.     In  all 
such  compounds  we  find  the  two  kinds  of  ions,  the  nega- 
tive or  anions  neutralizing  the  positive  or  kathions. 

14.  Relation  to  Valence.  —  From  this  we  see  that  atoms 
having  a  valence  of  two,  as  calcium,  for  example,  would 
carry  double  the  electricity  that  an  atom  like  chlorine 
would  with  a  valence  of  one.     In  other  words,  in  calcium 
chloride,  CaCl2,  the  calcium  ion  has  a  positive  charge  equal 
to  the  negative  charge  carried  by  the  two  ions  of  chlorine. 

SUMMARY  OF   CHAPTER 

Valence  —  Meaning  of  term. 

Illustrations. 
Classification  of  elements  as  to  valence. 

Synonymous  terms  for  univalent,  etc. 
Variation  in  valence. 


WATER  29 


Unsaturated  compounds. 

Real  —  Illustrations  of. 
Valence  of  radicals. 

Illustrations. 
Application  of  a  knowledge  of  valence. 

Writing  formulae  of  compounds. 

Relation  to  ionic  theory. 


CHAPTER  III 
WATER  :  H20 

1.  Its  Abundance. —  Water  is  one  of  the  most  abundant 
substances  known ;   it  covers  about  three-fourths  of  the 
surface  of  the  earth,  besides  existing  in  vast  quantities  in 
other  forms.     In  the  arctic  regions  in  the  form  of  an  ocean 
of  compressed  snow  it  covers  the  entire  surface  of  the  land 
to  a  depth  of  many  feet;  in  a  similar  form  it  caps  all  the 
loftiest  mountain  peaks  from   which  great  rivers  of  ice 
flow  down  the  valleys  until  they  are  melted  at  the  snow- 
line.     In  the  form  of  vapor  it  exists  in  the  atmosphere, 
invisible  except  when  condensed  in  fogs,  clouds,  etc.     In 
any  given  locality  this  moisture  in  the  air  varies  largely 
at  different  times,  but  not  often  is  there  more  than  sixty- 
five  per  cent  of  what  the  air  is  able  to  hold.     Even  with 
this  amount,  however,  it  has  been  estimated  that  were  the 
vapor  in  the  air  all  condensed,  it  would  form  over  the 
surface  of  the  entire  earth  a  layer  of  water  five  inches 
deep. 

2.  The  human  body  is  about  sixty  per  cent  water,  and 
daily  throws  off  through  the  pores  and  from  the  lungs 
over  three  pounds  of  moisture.     Many  vegetable  articles 
of  food  contain  eighty  to  ninety  per  cent  of  water,  and 
some  even  more. 


30  MODERN  CHEMISTRY 

\\ 

3.  Water  of  Crystallization.  —  Water  also  exists  in  an- 
other  form  not  so  familiar  as  those  already  mentioned; 
that  is,  water  of  crystallization.     A  great  many  compounds 
in  solidifying  from  their  aqueous  solutions  take  up  a  con- 
siderable amount  of  water.     This  does  not  exist  in  a  free 
state  like  water  in  the  pores  of  a  sponge,  or  in  a  piece  of 
soft  wood  that  has  been  submerged  for  some  time,  but  is 
in  combination  —  crystallized  in  with  the  molecules  them- 
selves.    Such  substances  in  crystallizing  cause  the  disap- 
pearance of  a  considerable  amount  of  water,  which  may, 
however,  usually  be  obtained  again  by  subjecting  the  body 
to  a  greater  or  less  degree  of  heat.     Some  astronomers 
even  believe  that  the  absence  of  water  upon  the  moon  may 
be  accounted  for  by  the  fact  that  such  bodies  as  those 
mentioned  have  taken  it  all  up  in  crystallizing  from  their 
aqueous  solutions.     An  idea  of  the  amount  contained  by 
such  substances  may  be  gained  from  the  following  experi- 
ments. 

EXPERIMENT  12. —  Put  into  a  test-tube  a  crystal  of  native  gypsum 
and  heat  in  the  Bunsen  flame.  What  do  you  see  depositing  upon  the 
cooler  portions  of  the  tube  ?  How  is  the  crystal  of  gypsum  affected  ? 
Repeat  the  experiment,  using  borax  or  alum  instead  of  gypsum,  and 
state  results. 

EXPERIMENT  13.  —  Expose  to  the  air  for  several  hours  a  crystal  of 
ferrous  sulphate.  Notice  its  appearance  before  the  exposure;  how 
has  it  changed  in  the  air  ? 

4.  Efflorescent  Substances.  —  Many  such  substances  as 
xferrous  sulphate  and  copper  sulphate,  upon  being  exposed 

to  an  atmosphere  more  or  less  dry,  give  up  all  or  part  of 
their  water  of  crystallization ;  at  the  same  time  they 
usually  change  in  color  and  crumble  to  a  powder.  The 
process  is  the  same  as  when  the  substances  are  heated,  but 
not  so  rapid.  By  adding  water  to  them  the  color  is 


WATER  31 

usually  restored,  and  they  crystallize  as  before.  Such 
substances  as  these  that  give  up  their  water  of  crystalliza- 
tion to  the  air  are  said  to  be  efflorescent. 
*VJ.  Deliquescent  Substances.  —  There  is  another  class  of 
substances  which  have  the  power  of  abstracting  moisture 
from  the  air  or  surrounding  bodies,  and  of  dissolving  them- 
selves either  in  whole  or  in  part  in  this  moisture.  Such 
are  called  deliquescent  bodies.  A  familiar  example  of 
these  is  a  substance  commonly  sold  by  grocers  under  the 
name  of  "  lye,"  which  on  being  exposed  to  the  air  rapidly 
takes  up  moisture.  Another  noted  example  is  phospho- 
rus pentoxide,  a  white  solid  formed  when  phosphorus 
is  burned  in  the  air  or  oxygen ;  also  calcium  chloride  and 
caustic  potash. 

EXPERIMENT  14.  —  Put  into  a  dry  evaporating  dish  or  beaker  a 
small  lump  of  fused  calcium  chloride  and  allow  it  to  stand  several 
hours  or  over  night.  Notice  how  it  has  changed.  In  the  same  way 
expose  a  small  piece  of  caustic  potash.  Notice  how  rapidly  it  changes. 
Only  a  few  minutes  will  be  necessary  in  this  case. 

Common  salt,  stick  candy,  and  some  forms  of  taffy  are 
very  familiar  examples  of  deliquescent  bodies. 

6.  Distinguishing  Characteristics  of  Water.  —  In  the  pure 
state,  water  is  practically  colorless,  but  when  of  great 
depth  it  is  seen  to  be  of  a  blue  color.  It  is  odorless  and 
tasteless,  but  we  are  so  accustomed  to  drinking  impure 
water  that  when  we  use  that  which  is  distilled,  or 
perfectly  pure,  it  tastes- "flat,"  just  as  unseasoned  food 
does  to  those  who  are  habituated  to  the  use  of  salt, 
pepper,  and  other  condiments.  Pure  water,  on  being 
evaporated  to  dryness,  leaves  no  residue  whatever,  and 
this,  in  connection  with  the  fact  that  it  affects  vege- 
table coloring  matter  in  no  way,  is  one  method  of  test- 
ing it. 


32  MODERN  CHEMISTRY 


,  Solvent  Powers  of  Water.  —  Pure  water  is  seldom 
found,  owing  to  its  great  solvent  powers.  To  a  greater 
or  less  extent  it  may  be  said  to  be  almost  a  universal 
solvent.  Even  glass  and  similar  substances  immersed  in 
water  show  appreciable  loss  after  a  considerable  length  of 
time.  From  this  property  result  the  various  kinds  of 
"  hard "  or  mineral  waters,  medicinal,  saline,  etc.  It  is 
owing  to  the  solvent  powers  of  water,  and  the  fact  that 
evaporation  leaves  all  mineral  matter  behind,  that  the 
ocean  contains  such  vast  quantities  of  different  kinds  of 
salt. 

8.  For  example,  in  a  hundred  pounds  of  sea  water,  there 
are  over  three  pounds  of  solid  matter ;  of  this  the  greater 
portion  is  common  salt,  but  compounds  of  magnesium 
and  calcium  in  the  form  of  what  are  usually  known  as 
epsom  salts  and  gypsum  also  occur.  It  has  been  estimated 
that  if  the  ocean  were  of  an  average  depth  of  one  thousand 
feet,  the  common  salt  in  solution  would  occupy  a  space  of 
about  three  and  a  half  million  cubic  miles,  or  a  volume 
more  than  five  times  as  great  as  that  of  the  Alps.  On 
this  basis,  if  the  depth  of  the  ocean  averages  what  is  now 
claimed  for  it,  the  amount  of  salt  surpasses  in  bulk  our 
greatest  mountain  ranges. 

Qj>"  Composition  of  Water.  —  By  many  of  the  ancients, 
water,  along  with  fire  and  air,  was  regarded  as  an  element; 
but  about  1800  A.D.  it  was  proved  to  be  a  compound  body. 
There  are  two  methods  of  proof,  which  taken  together 
are  quite  conclusive.  • 

The  first  proof  is  by  Electrolysis. 

EXPERIMENT  15. —  Fill  the  tubes  of  the  electrolytic  apparatus 
shown  in  Fig.  3  with  water  slightly  acidulated  with  sulphuric  acid, 
the  latter  being  added  simply  to  increase  the  conductivity.  Then 
connect  the  platinum  electrodes  with  a  strong  battery.  As  the 


WATER 


33 


current  passes  through  the  water,  bubbles  of  gas  will  be  seen  rising 
from  the  two  strips  of  platinum,  P,  and 
from  one  of  them  considerably  faster 
than  from  the  other.  It  will  be  found 
that  twice  as  much  gas  collects  in  one 
tube  as  in  the  other.  These  two  gases, 
we  shall  learn  before  long,  are  hydro- 
gen and  oxygen.  Open  the  stop-cock 
of  the  tube  containing  the  greater 
amount  of  gas,  and  hold  a  lighted 
match  to  it ;  notice  that  it  burns  with 
a  very  pale  flame.  Test  the  gas  in  tho 
other  tube,  using  a  pine  splinter  with 
a  spark  upon  the  end;  notice  that  it 
bursts  into  a  flame.  FIG.  3. 

xtt).    The  second  proof  is  by  Synthesis. 

EXPERIMENT  16.  —  Put  into  the  eudiometer,  Fig.  4,  8  cc.  of  oxy- 
gen, and  twice  as  much  or  more  hydrogen,  the  instrument   being 

already  partly  filled  with  mercury,  M. 
Hold  the  thumb  over  the  open  end  and 
pass  a  spark  from  a  galvanic  battery. 
*  The  two  gases  will  combine  with  ex- 
plosive force,  producing  water  in  the 
form  of  vapor.  If  the  proportions  were 
exactly  two  of  hydrogen  to  one  of  oxy- 
gen, when  the  apparatus  has  become 
cool,  there  will  be  no  gaseous  residue, 
showing  that  the  two  unite  in  this  pro- 
portion to  form  water.  A  in  the  figure 
is  a  cushion  of  air  left  to  break  the  force  of  the  explosion. 


FIG.  4. 


11.  Conclusions.  —  From  the  above  experiments  we 
learn  that  water  is  the  result  of  the  union  of  two  invisible 
gases,  one  of  which  burns  with  a  pale  flame,  the  other  of 
which  causes  various  substances  to  burn  vigorously.  We 
see  also  that  from  the  union  of  the  two  gases,  which  to- 
gether form  a  very  explosive  mixture,  there  results  an 


34 


MODERN  CHEMISTRY 


exceedingly  stable  compound,  which  not  only  does  not 
burn,  but  which  has  the  power  of  quenching  thirst  and  of 
overcoming  the  greatest  fires.  These  two  gases  were 
given  the  names,  hydrogen  and  oxygen. 

12.  We  noticed   also   in   the   proof  by   analysis,  that 
the  hydrogen  was  given  off  in  volume  double  that  of  the 
"oxygen,  and  further,  that  in  mixing  the  two  gases  for  the 
synthetic  proof  we  caused  them  to  unite  in  the  same  ratio. 
From  theso  experiments  we  may  conclude  that  the  com- 
position of  water  by  volume  is  two  parts  of  hydrogen  to 
one  of  oxygen,  a  fact  which  we  represent  by  the  expression 
H20. 

13.  Analysis  by  Other  Methods.  —  The  analysis  of  water 
may  be  effected  by  means  other  than  electricity.      For 
example,  if  a  current  of  steam  is  made  to  pass  through  a 
tube  containing  charcoal  or  coke  heated  red  hot,  the  steam 
is  decomposed  ;  the  oxygen  combines  with  the  carbon  of 
the  charcoal,  forming  an  oxide  of  carbon,  and  at  the  same 
time  the  hydrogen  is  set  free. 

14.  Synthesis  by  Other   Methods.  —  In  a  similar  way 
the  synthesis  of  water  may  be  effected.     If  a  current  of 
hydrogen  is  passed  through  a  tube  containing  some  me- 
tallic oxide,  heated  to  redness,  for  example,  copper  oxide, 
the  oxygen  is  removed  from  the  compound  by  means  of 
the  hydrogen,  and  water  is  formed  and  may  be  collected. 

EXPERIMENT  17.  —  Into  a  of  the  small  bulb-tube  put  a  little  black 

oxide  of  copper,  and  weigh 
both  tube  and  oxide  care- 
fully. Next  fill  a  U-shaped 
tube  with  lumps  of  calcium 
chloride,  weigh  and  quickly 
connect  with  the  other  tube. 
Now  pass  a  current  of  hy- 
FIG.  5.  drogen,  generated  as  on 


WATER  35 

page  39,  over  the  copper  oxide,  heated  to  redness.  The  hydrogen 
should  first  be  dried  by  passing  through  sulphuric  acid  or  over  calcium 
chloride.  After  some  time,  disconnect  the  apparatus,  and  weigh  the 
U-tube ;  the  gain  in  weight  will  represent  the  amount  of  water  pro- 
duced. When  the  bulb-tube  is  cool,  weigh  it :  the  loss  will  represent 
the  amount  of  oxygen  removed.  Subtracting  the  weight  of  the  oxygen 
from  the  weight  of  water  found  will  give  the  amount  of  hydrogen. 
Allowing  for  errors,  this  should  give  eight  parts  of  oxygen  to  one  of 
hydrogen,  by  weight. 

From  this  experiment  we  are  able  to  conclude  as  to  the  quantita- 
tive composition  of  water,  just  as  by  the  others  we  learned  of  the 
volumetric.  The  action  of  hydrogen  in  thus  removing  oxygen  from 
an  oxide  is  called  reduction. 

Water  I  By  volume:  HJdrogen»  25  Oxygen,  1. 
(  By  weight :  Hydrogen,  1 ;  Oxygen,  8. 


SUMMARY  OF  CHAPTER 

Water  —  Various  forms  in  which  it  occurs. 
Water  of  crystallization. 
Meaning  of  term. 

Examples  of  substances  containing  it. 
Proof  of  its  presence  by  experiment. 
Efflorescent  substances. 
Deliquescence  —  Meaning  of  term. 

Illustrations. 

Some  special  characteristics  of  water. 
Composition  of  water  —  Proof  of. 

a.  By  analysis —  Details  of  work. 

Apparatus  used. 

b.  By  synthesis  —  Explanation  of  process. 

Drawing  of  apparatus. 
Composition  by  weight. 
Proof  by  experiments. 


y 

CHAPTER  IV 

^r 

HYDROGEN  :  H  =  1 

1.  History.  —  The  term  hydrogen  is  from  two  Greek 
words,  which   mean   water  producer,  and   the  gas  is  so 
named   because  this  element  enters  so  largely  into  the 
composition  of  water.     It  was  first  isolated  in  quantities 
sufficient  for  experiment  by  Cavendish  in  1766,  and  on 
account  of  its  combustibility  was  called  by  him  inflam- 
mable air. 

2.  Where  found.  —  Hydrogen  is  seldom  found  uncom- 
bined,  though  its  chemical  affinity  for  most  substances  is 
not  very  marked.     It  exists  abundantly  in  composition  — 
water  being  the  most  important  example  ;  it  enters  into 
nearly  all  organic  compounds  ;    it  is  given  off,  together 
with  other  gases,  by  some  volcanoes  ;  and  by  the  spectro- 
scope we  know  that  it  exists  in  the  atmospheres  of  the  sun 
and  of  some  of  the  stars. 

3.  Methods   of   obtaining    Hydrogen.  —  We   have   seen 
already  in    Experiment   15   that   hydrogen   may  be   ob- 
tained by  the  electrolysis  of  water.      This  gives  a  very 
pure  gas,  but  does  not  produce  it  rapidly  enough   for 
ordinary  experimental  purposes.     Just  as  electricity  has 
the  power  of  decomposing  water,  so  do  certain  metals. 
When  iron  is  exposed  to  moisture,  we  say  it  rusts;   in 
reality,  it  takes  up  a  certain  amount  of  oxygen  from  the 
water  and  sets  free  a  corresponding  amount  of  hydrogen.* 

*  Rust  is  an  oxide  of  iron ;   that  is,  a  compound  of  iron   and  oxy- 
gen, represented  by  the  formula  Fe203.     The  chemical  change  which 

36 


HYDROGEN  37 

4.  Decomposition    of   Water.  —  Again,   there   are   some 
metals,  like  calcium,  a  constituent  of  common  limestone, 
which  have  the  power  of  decomposing  water  at  the  boiling 
point,  setting  free  a  part  of  the  hydrogen  and  forming  at 
the  same  time  a  compound,  such  as   lime  water.      The 
•chemical    action    may   be    expressed    by    the    following 
equation  :  — 

Ca  +  2  H20  =  Ca  (OH)2  +  H2. 

5.  There  are  two  common  metals,  sodium  and  potas- 
sium, which  decompose  water  rapidly  at  ordinary  tempera- 
tures.    Of  these,  the  second  acts  much  more  violently, 
generating  almost  instantly  sufficient  heat  to  ignite  the 
hydrogen  given  off  from  the  water  and  volatilizing  a  por- 
tion of  the  metal  itself.     This  is  seen  in  the  violet  color 
which  is  imparted  to  the  flame.     That  sodium  is  setting 
free  a  combustible   gas   in   the  same 

way  may  be  shown  by  bringing  a 
lighted  match  close  to  the  metal, 
when  the  hydrogen  will  be  ignited  as 
it  was  spontaneously  with  potassium. 

EXPERIMENT  18.  —  Fill  a  test-tube  with 
water  and  invert  it  over  a  trough  or  basin  of 
water,  as  shown  in  Fig.  6.  Put  into  a  wire 
gauze  spoon,  or  wrap  in  a  piece  of  flexible  wire  FIG.  6. 

probably  takes  place  when  iron  is  thus  exposed  may  be  expressed  as 
2  Fe  +  6  H20  =  6  H  +  Fe2O3,  3  H2O, 

in  which  Fe2O3  is  rust.  Likewise,  if  iron  filings  be  heated  red  hot,  and 
a  current  of  steam  slowly  passed  over  them,  the  filings  take  up  the  oxygen 
from  the  steam  and  are  converted  into  an  oxide  of  iron,  Fe304,  differing 
somewhat  from  rust,  while  hydrogen  is  set  free.  The  following  equation 
expresses  the  chemical  changes  that  take  place  :  — 

3  Fe  +  4  H2O  =  Fe3O4  +  4  H2. 


38 


MODERN  CHEMISTRY 


cloth,  a  small  piece  of  sodium  and  hold  under  the  mouth  of  the  tube. 
Bubbles  of  gas  will  rapidly  form,  will  rise  into  the  tube  and  displace 
the  water.  Test  the  gas  obtained  to  see  whether  it  acts  as  did  the 
hydrogen  obtained  by  electrolysis  in  Experiment  15.  Does  it  seem  to 
be  the  same  kind  of  gas?  Sometimes,  before  putting  the  sodium 
into  water,  it  is  treated  with  a  small  quantity  of  mercury,  whereby 
the  rapidity  of  the  action  is  greatly  decreased. 

6.  Caustic  Soda.  —  The  chemical  change  which  has 
taken  place  in  the  above  experiment  may  be  expressed 
as  follows  :  — 


or,  as  it  is  usually  and  most  simply  written,  — 
H20  +  Na  =  NaOH  +  H. 

The  graphic  equation  above  shows  that  in  each  molecule 
of  water  one  atom  of  the  hydrogen  is  replaced  by  one  of 
sodium,  represented  by  Na,  and  that  thus  a  new  compound, 
NaOH,  called  caustic  soda  or  sodium  hydroxide,  is  formed. 
In  other  words,  the  water  molecule  becomes  one  of  caustic 
soda,  thus :  — 


becomes 


7.  Proof  of  the  Above.  —  The  equation  written  above  is 
not  a  matter  of  theory,  but  is  determined  by  experiment. 
Add  a  drop  of  phenolphthalein  to  the  water  in  which  the 
sodium  was  placed.  In  the  same  way,  test  a  solution  of 


HYDROGEN 


39 


caustic  soda ;   also  a  little  pure  water  in  another  tube. 
What  are  the  results? 

8.  Other  Methods  of  obtaining  Hydrogen.  —  The  above 
methods  of  obtaining  hydrogen,  while  of  interest,  are  too 
expensive  where  considerable  quantities  are  needed  for 
experimental  work.     All  acids  contain  hydrogen,  and  just 
as  some  metals  decompose  water,  so  certain  others  act  with 
acids. 

9.  Laboratory    Method.  —  In  obtaining  hydrogen  for 
laboratory  purposes  this  is  the  plan  usually  pursued.     The 
metal  used  is  generally  iron  or  zinc,  and  the  acid,  sulphuric 
or  hydrochloric. 

EXPERIMENT  19.  —  Fit  to  a  flask  a  cork  doubly  perforated.  Through 
one  of  the  holes  insert  a  delivery  tube,  and  through  the  other  a  this- 
tle tube  which  extends 
nearly  to  the  bottom  of 
the  flask.  Put  into  the 
flask  several  pieces  of 
granulated  zinc  made  by 
pouring  the  metal  in  a 
molten  condition  into 
cold  water.  Add  water 
until  the  zinc  is  nearly 
covered,  and  then  pour 
in  slowly  a  small  quan- 
tity of  strong  sulphuric 
acid.  After  allowing  the 
first  gas  which  comes 
over  to  escape,  because  it  is  mixed  with  air,  collect  several  bottles  over 
water  as  described  on  page  362  and  preserve  for  experiments  a  little 
later.  The  action  may  be  hastened  by  adding  a  little  copper  sulphate 
to  the  flask  a  few  minutes  before  the  acid  is  introduced. 

10.  The  Chemical  Reaction.  —  It  will  be  noticed  that 
the  zinc  in  the  above  experiment  gradually  disappears. 
We  shall  find  by  testing  the  gas  which  is  evolved  that 


FIG.  7.  —  Hydrogen  Apparatus. 

p  =  pan.  g  =  generating  flask. 

t  =  thistle  tube.          r  =  receiving  flask. 

d  =  deli  very  tube. 


40  MODERN  CHEMISTRY 

it  is  hydrogen.  But  what  remains  in  the  flask  ?  When 
the  action  has  ceased,  decant  or  filter  off  the  clear  solu- 
tion from  any  pieces  of  zinc  or  sediment,  evaporate  over 
a  cup  or  beaker  of  boiling  water  nearly  to  dryness,  and 
allow  to  cool.  Drain  off  from  the  crystals  any  liquid 
remaining,  rinse  with  a  little  cold  water,  and  dry  them. 
To  prove  that  they  are  zinc  sulphate,  see  pages  181  and 
338.  We  may  then  express  the  changes  thus  :  — 


or  Zn  +  H2S04  =  ZnSO4  +  H2. 

Zinc  sulphate  is  a  white  compound  which  collects  upon 
the  zinc,  and  would  soon  cover  it  so  completely  as  to  stop 
the  chemical  action  ;  the  water,  however,  being  added  dis- 
solves it  as  fast  as  formed,  and  leaves  a  clean  surface 
exposed  to  the  acid. 

11.  Method  of  obtaining  Large  Quantities. — When  hydro- 
gen is  desired  in  very  large  quantities,  as  in  filling  balloons, 
iron,  being  cheaper,  is  used  instead  of  zinc.     The  gas  thus 
obtained  is  somewhat   less  pure,   but  it  is  not   on   this 
account  specially  objectionable.     Large  vessels  or  retorts 
are  used,  which  are  lined  with  lead,  a  metal  which  is  not 
affected  by  dilute  sulphuric  acid.     The  hydrogen  obtained 
is  passed  through  water  and  lime  to  purify  it,  after  which 
it  is  transferred  to  the  balloon. 

12.  Mond's   Method.  —  This   method,    although    it   has 
thus  far  been  used  only  to  a  limited  extent,  promises  to 
give   satisfaction.      We   have   seen   that  when   steam  is 


HYDEOGEN 


41 


passed  over  red-hot  charcoal  the  former  is  decomposed 
just  as  when  passed  over  red-hot  iron  (page  37)  and  two 
similar  products  are  formed,  both  gases  ;  thus,  — 

H2O  +  C  =  H2  +  CO. 

The  apparatus  may  be  represented  conventionally  as 
follows :  — 


FIG.  8.  —  Mond's  Method. 

F  is  a  furnace,  B  the  boiler  in  which  the  steam  is  generated,  C  a 
tube  containing  lumps  of  coke  which  are  heated  red  hot  by  a  gas 
furnace  beneath,  Ni  a  tube  containing  powdered  metallic  nickel,  L  an 
apartment  containing  lime  water.  The  steam  passing  through  C  is 
decomposed  as  stated  above ;  the  mixture  of  hydrogen  and  carbon 
monoxide  formed  here  passes  over  the  nickel,  also  heated  red  hot.  In 
this  tube  a  part  of  the  carbon  unites  with  the  nickel,  and  carbon 
dioxide  is  formed.  This  mixed  with  the  hydrogen  passes  on  through 
the  "  washer "  L,  containing  lime  water,  which  absorbs  the  carbon 
dioxide,  leaving  the  hydrogen  comparatively  pure.  The  reactions  hi 
the  different  parts  of  the  process  may  be  shown  as  follows :  — 

H2O  +  C  =  H2  +  CO  (in  the  coke  tube). 
H2  +  2  CO  -f  Ni  =  NiC  +  H2  +  CO2  (in  the  nickel  tube). 
H2  +  CO2  +  Ca(OH)2  =  H2  +  CaCO3  +  H2O  (in  the  "  washer  "). 

The  nickel  carbide  formed  is  readily  converted  back  again  into 
metallic  nickel  by  heating  in  the  air,  so  that  it  may  be  used  over  and 
over, 


42 


MODERN  CHEMISTRY 


13.  Characteristics  of  Hydrogen.  —  The  following  experi- 
ments will  illustrate  well  the  most  striking  peculiarities 
of  hydrogen  :  — 

EXPERIMENT  20.  —  Remove  one  of  the  bottles  of  hydrogen  from 
the  water,  keeping  it  inverted,  and  thrust  up  into  it  a  burning  candle. 
Notice  whether  the  candle  continues  to  burn  in  the  gas  ;  notice  also 
what  happens  as  you  remove  it  again.  Can  you  see  anything  burning 
at  the  mouth  of  the  bottle? 

EXPERIMENT  21.  —  To  show  the  lightness  of  hydrogen.  Bring  a 
bottle  of  the  gas,  a,  mouth  downward,  up 
close  to  another  inverted  bottle,  t,  of  about 
the  same  size.  Then  gradually  tip  the 
hydrogen  bottle,  a,  as  shown  in  Fig.  9,  just 
as  you  would  pour  water  from  one  vessel 
into  another,  only  in  a  reverse  order. 

Now  test  both  bottles  to  learn  which  con- 
FIG.  9.  -  Upward  Decantation. 


hydrogen>     gtate  the  results< 

EXPERIMENT  22.  —  Start  the  generator  again,  and  replace  the  de- 
livery tube  with  one  which  has  been  drawn  to  a  fine  jet.  Let  the 
gas  flow  a  few  minutes  until  the  air  is  all  expelled,  and  then  ignite  it. 

14.  CAUTION.  —  A  mixture  of  air  and  hydrogen  is  very 
explosive,  and  before  lighting  the  jet  a  towel  should  be 
wrapped  about  the  generating  flask.  It  will  do  equally 
well  to  inclose  the  flask  in  a  pasteboard  box  as  shown  in 
the  figure. 

When  first  lighted,  how  does  the  hydrogen  burn  ?     How  does  it 
soon  change?     This  is  due  to  the  sodium  in  the  glass,  which  colors 
the  flame.     A  burning  jet  of  hydrogen  is  some- 
times called  the  "  philosopher's  lamp."     Does  the 
gas  burn  with  much   heat  ?     Hold  a  clean  dry 
bottle  or  test-tube  over  the  flame.     Do  you  see 
any  deposit  forming  upon  the  upper  part  of  the 
tube?   What  is  it?    Now  try  several  tubes  and  bot- 
tles of  different  sizes  in  the  same  way  ;  notice  the 
different  pitch  of  the  "singing  tones"  produced. 
FIG  10  —  Hvdroaen    When  the  tube  is  thus  sounding,  notice  the  flame 
Jet  m  Bo*.  carefully.     Can  you  explain  the  tones  produced  ? 


HYDROGEN  43 

EXPERIMENT  23.  —  Allow  a  jet  of  hydrogen  from  a  generator  work- 
ing rapidly  to  strike  against  a  platinum  sponge.  State  the  results. 

EXPERIMENT  24. —  The  hydrogen  pistol  shows  the  explosiveness 
of  a  mixture  of  air  and  hydrogen.*  Load  the  pistol  by  pouring  into 
it  a  small  bottle  of  hydrogen,  as  shown  in  Experiment  21,  and  fire  by 
bringing  a  flame  to  the  touch-hole.  A  loud  explosion  should  follow. 

EXPERIMENT  25.  —  Hydrogen  soap-bubbles  —  to  show  lightness  of 
hydrogen.  For  success  in  this  experiment  a  good  soap  solution  is 
necessary.  To  a  little  soft  water  add  a  few  shavings  of  castile  or 
other  good  soap,  and  when  dissolved  add  about  one-third  as  much 
glycerine  as  soap  solution.  Shake  well.  Now  attach  to  a  delivery 
tube,  from  which  is  flowing  a  current  of  hydrogen,  a  clay  pipe,  or  even 
an  ordinary  spool ;  dip  into  the  soap  solution,  and  let  the  bubble  form 
in  the  usual  way.  Detach  from  the  pipe  by  a  gentle  jerk  and  notice 
whether  the  bubble  rises  or  falls.  Touch  a  light  to  one  of  the  bubbles. 
What  happens?  This  experiment  is  sometimes  made  more  striking 
by  filling  the  bubble  with  a  mixture  of  hydrogen  and  oxygen,  which, 
when  touched  with  a  flame,  explodes  violently. 

15.  CAUTION.  —  The  greatest  care  must  be  taken  to  avoid 
bringing  the  flame  near  the  delivery  tube,  lest  the  whole 
mixture  be  exploded  with  serious  results. 

EXPERIMENT  26,  —  To  show  the  presence  of  hydrogen  in  oils,  alco- 
hol, etc.  We  have  already  seen  that  when  hydrogen  burns,  water  is 
produced.  This  is  true  whether  we  have  hydrogen  free,  or  in  the 
form  of  compounds.  Light  a  small  candle  and  hold  over  it  a  cold 
beaker.  Notice  the  water  condensing  upon  the  cooler  portions  of  the 
beaker.  In  the  same  way  try  a  small  spirit  lamp.  State  the  results. 

16.  Conclusions  from  our  Work   with   Hydrogen.  —  By 

the  above  work  with  hydrogen  we  have  learned  that  it  is 
a  colorless  gas  ;  is  without  odor  if  pure,  and  very  light. 

*  The  pistol  may  easily  be  made  from  a  small  tin  can.  With  an  awl 
punch  a  hole  in  the  side  of  the  can  near  the  bottom,  and  for  a  bullet  use 
a  cork  snugly  fitted  to  the  mouth  of  the  can.  When  a  light  is  brought  to 
the  touch-hole,  several  seconds  may  elapse  before  the  explosion  follows, 
but  the  experiment  almost  invariably  succeeds. 


44 


MODERN  CHEMISTRY 


Its  density  is  but  little  more  than  one-fifteenth  that  of 
air.  It  is  this  which  causes  it  to  diffuse  so  rapidly,  and 
renders  it  valuable  for  filling  balloons.  A  liter  of  the  gas 
weighs  .0896  g.  It  is  very  inflammable,  and  burns  with 
a  pale,  almost  non-luminous  flame.  As  noticed  above,  the 
hydrogen  flame  from  a  glass  jet  has  a  yellow  color,  but  this 
is  due  to  a  compound  of  sodium  in  the  glass,  just  as  the 
hydrogen  arising  from  the  sodium  on  the  water  burned 
with  a  yellow  flame.  The  heat  of  this  flame  is  intense, 
as  is  seen  by  the  rapidity  with  which  the  glass  jet  becomes 
red  hot.  When  hydrogen  burns  in  the  air  or  in  oxygen, 
water  is  the  only  product,  the  union  being  expressed  by 
the  following  equation :  — 


or, 


2H 


O2        =   2H20. 


17-    Combination  of  Hydrogen  with  Other  Substances.  — 

The  explosiveness  of  hydrogen  when  mixed  with  oxygen 
has  already  been  noticed.  One  of  its  most  remarkable 
properties  is  that  of  being  absorbed  or  occluded  by  certain 
metals.  By  finely  divided  platinum  the  absorption  is  so 
rapid  that  the  metal  becomes  red  hot,  and  the  jet  of 
hydrogen  is  quickly  ignited.  Likewise,  if  a  piece  of 
spongy  platinum  be  lowered  into  a  mixture  of  hydrogen 
and  oxygen,  the  rapid  absorption  in  a  short  time  causes 
sufficient  heat  to  explode  the  mixture. 

At   the   usual    temperature,   hydrogen   has  very  little 


HYDROGEN  45 

affinity  for  most  substances.  As  will  be  seen  in  Experi- 
ment 65,  it  explodes  violently  when  mixed  with  chlorine, 
either  on  the  approach  of  a  strong  light  or  by  means  of  a 
spark.  It  unites  vigorously  with  oxygen  also"  on  the 
application  of  a  flame,  but  a  light  has  no  effect. 

18.  Liquid  Hydrogen.  —  Hydrogen  is  one  of  the  most 
difficult  gases  to  reduce  to  the  liquid  condition.     This  has 
been  accomplished,  however,  by  reducing  the  temperature 
to  —205°  C.,  and  allowing  it  to  escape  rapidly  from  a  pres- 
sure of  180  atmospheres  into  a  vacuum.    At  the  same  time 
this  space  is  surrounded  by  a  temperature  of  —200°  C. 
Considerable  quantities  have  been  obtained  in  this  way. 
In  April  of  the  year  1900,  Dewar  even  succeeded  in  solidi- 
fying the  gas.     He  surrounded  liquid  hydrogen  with  lique- 
fied air,  and  then  by  a  pump  caused  so  rapid  an  evaporation 
of  the  hydrogen  that  he  soon  obtained  the  remainder  in  a 
white,  opaque  solid. 

19.  Uses  of  Hydrogen.  —  As  a  gas  it  has  but  few  prac- 
tical uses.     Its  suitability  for  filling  balloons  has  been 
mentioned,  but  in  such  cases  it  is  generally  used  in  a  very 
impure  form,  mixed  with  various  hydro-carbons  given  off 
with  the  hydrogen  in  the  later  distillation  of  coal.     In  the 
nascent  state,  that  is,  at  the  instant  it  is  set  free  from  some 
compound,  it  has  great  chemical  activity  and  has  the  power 
of  reducing  many  metals  from  their  compounds.      This 
use  has  already  been  seen  in  the  passage  of  hydrogen  over 
copper  oxide,  and  will  be  further  illustrated  in  our  work 
with  silver,  iron,  and  other  metals.* 

*  The  use  of  hydrogen  in  an  automatic  cigar-lighter  is  occasionally  seen. 
As  shown  in  the  figure,  a  small  glass  cylinder  has  a  cubical  block,  a,  of 
porcelain  in  the  bottom  :  upon  this  rests  an  inverted  glass  cylinder,  c, 
with  a  tubular  neck  and  stop-cock,  s ;  above  this  jet  is  supported  a  plat- 
inum sponge,  p\  under  the  small  cylinder  upon  the  porcelain  block  is 


46 


MODERN  CHEMISTRY 


SUMMARY  OF   CHAPTER 

Hydrogen  —  Origin  of  term  and  meaning. 
Occurrence  of  hydrogen. 
Methods  of  making  hydrogen. 
By  decomposing  water. 

With  sodium  or  potassium. 
Describe  method  and  apparatus. 
Chemical  action  —  Proof  of,  by  experiment. 
By  decomposing  acids. 
With  zinc. 

Draw  apparatus  and  explain  method. 
Commercial  methods. 

For  filling  balloons. 
Characteristics  of  hydrogen. 
Experiments  to  illustrate. 
Density. 
Inflammability. 
Explosiveness,  etc. 
Liquid  hydrogen. 
Uses  of  hydrogen. 
Special  points. 

Explain  the  hydrogen  pistol. 
Philosopher's  lamp. 
Singing  flame. 


FIG.  11. 


placed  some  zinc,  z,  and  in  the  outer  cylinder 
diluted  sulphuric  acid.  As  the  acid  and  zinc 
react  upon  each  other,  hydrogen  fills  the  in- 
verted cylinder,  forces  out  the  acid,  and  the 
action  ceases.  If  now  the  stop-cock  is  opened, 
the  hydrogen  flows  out  of  the  jet,  the  acid 
reenters,  and  the  generation  of  gas  continues. 
As  already  seen,  the  hydrogen  jet  is  quickly 
ignited  by  the  platinum.  When  the  customer 
has  lighted  his  cigar,  the  stop-cock  is  again 
turned,  and  the  action  soon  ceases.  It  ought 
to  be  said,  perhaps,  that  such  apparatus  is 


of  more  interest  as  a  novelty  than  as  of  real  lasting  utility. 


; 


CHAPTER  V 

4  / 

OXYGEN,  COMBUSTION,  OZONE 
OXYGEN  :  0  =  16 

1.  Its  Discovery.  —  The  term  oxygen  is  derived  from 
two  Greek  words,  meaning  acid-former,  and  was  given  to 
this  element  because  it  was  believed  to  be  essential  to 
the  production  of  all  acids.     Oxygen  was  discovered  by 
Scheele  in  1773,  but  he  did  not  publish  his  discovery  until 
1775  ;  and  as  in  the  meantime  Priestley  had  isolated  the 
same  gas  and  had  published  an  account  of  his  experiments, 
the  latter  is  generally  given  the  credit. 

2.  Abundance  of  Oxygen.  —  Oxygen   is   found   in   the 
atmosphere  in  large  quantities,  uncombined,  constituting 
about  one-fifth  of  the  whole.     It  has  been  estimated  that 
there   is   in  the  atmosphere  alone  over  two  and  a  half 
million  billions  of  pounds.      A  liberal   estimate   of   the 
amount  used  annually  in  respiration,  and  all   forms   of 
combustion,  is  about  two  and  a  quarter  billion  pounds. 
At  this  rate,  in  a  century  the  entire  world  would  use  only 
one  ten  -thousandth  part  of  the  whole.     At  the  same  time 
it  must  be  remembered  that  plant  life  is  pouring  the  oxy- 
gen back  again  into  the  air,  so  that  there  is  no  danger  of 
the  equilibrium  being  destroyed.     Oxygen  also  forms  by 
weight  eight-ninths  of  water,  and  being  absorbed  by  the 
same,  exists  therein  in  considerable  quantities  in  a  free 
state.     It  is  this  free  oxygen  which  is  breathed  by  fishes. 
On  account  of  its  great  affinity  for  other  substances,  it  is 

47 


48 


MODERN  CHEMISTRY 


found  in  combination  with  nearly  all  known  elements,  and 
forms  in  this  way  about  45  to  50  per  cent  of  the  earth's 
crust. 

3.  How  to  produce  Oxygen.  —  As  a  matter  of  historical 
interest,  the  method  employed  by  Priestley  is  still  some- 
times used.     It  is  as  follows  :  — 

EXPERIMENT  27. —  Place  in  a  hard-glass  test-tube  about  a  half 
gram  of  mercuric  oxide,  HgO,  and  heat  strongly.  Notice  the  change 
in  the  appearance  of  the  oxide.  Insert  into  the  tube  a  pine  splinter 
with  a  spark  upon  the  end.  What  happens?  What  do  you  notice 
collecting  upon  the  sides  of  the  tube?  What  substances  have  there- 
fore been  obtained  by  heating  this  oxide  ? 

4.  Explanation.  —  The  heat  used  has  served  to  decom- 
pose the  molecules  of  mercuric  oxide  into  their  constituent 
parts,  thus  :  - 


-f  HEAT  — 


or, 


2  HgO  +  heat  =  2  Hg  +  O2. 


The  two  molecules  of  red  oxide  of  mercury  have  yielded 
two  molecules  of  mercury,  one  atom  in  each,  and  one 
molecule  of  oxygen,  having  two  atoms.  By  continuing 
the  operation  the  entire  amount  of  the  red  oxide  would 
disappear,  while  the  deposit  of  mercury  upon  the  sides  of 
the  tube  would  gradually  increase. 

5.  Other  Methods  of  obtaining  Oxygen. — The  above 
method,  though  of  interest,  furnishes  too  limited  a  quan- 
tity of  oxygen  for  practical  purposes.  A  better  and  more 


OXYGEN,   COMBUSTION,   OZONE 


49 


common  way  is  to  heat  potassium  chlorate,  KC1O3,  with 
manganese  dioxide,  MnO0. 


AST 

l_ 

FIG.  12. 


EXPERIMENT  28.  —  Mix  together  in  a  good-sized  test-tube,  or  small 
flask,  1  or  2  g.  of  potassium  chlorate  and  half  as  much  manganese 
dioxide.  Support  upon  a  ring-stand 
with  a  wire  screen  protection,  as  shown 
in  the  accompanying  figure,  and  attach 
the  cork  and  delivery  tube.  Heat  gen- 
tly at  first,  and  then  more  strongly,  but 
moderately,  so  as  to  regulate  the  flow 
of  gas  and  not  let  it  become  too  rapid. 
Allow  the  first  that  comes  over  to 
escape,  then  collect  several  bottles  of 
the  gas  over  water  as  you  did  the  hydro- 
gen, and  use  for  the  following  experi- 
ments. Save  the  contents  of  the  flask 
for  further  use. 

EXPERIMENT  29.  —  Slip  a  sheet  of  glass  or  paper  under  a  small 
bottle  of  oxygen,  and  place  it  in  an  upright  position  upon  the  table. 
Now  plunge  into  the  oxygen  a  taper,  or  pine  splinter,  with  a  spark 
upon  it.  Do  you  obtain  the  same  results  as  before  in  the  case  of  the 
oxide  of  mercury  ? 

EXPERIMENT  30.  —  Into  another  bottle  of  oxygen  lower  a  deflagrat- 
ing spoon  containing  some  burning  sulphur;  does  it  burn  any  differ- 
ently than  in  the  air?  If  no  deflagrating  spoon  is  at  hand,  the  student 
can  prepare  one  by  hollowing  put  the  end  of  a  short  stick  of  gas 
carbon,  or  of  crayon,  and  attaching  a  wire  handle  of  suitable  length. 

EXPERIMENT  31.  —  Fasten  a  piece  of  soft  or  bark  charcoal  to  a 
stout  iron  wire,  hold  it  in  the  burner  flame  until  it  begins  to  glow, 
then  plunge  into  a  jar  of  oxygen.  If  the  charcoal  is  soft,  the  results 
will  be  very  striking.  Describe  them. 

EXPERIMENT  32.  —  Twist  together  three  or  four  fine  iron  wires, 
fasten  to  the  end  a  small  pine  splinter,  or  warm  and  dip  into  sulphur 
and  ignite.  Plunge  quickly  into  a  large  jar  of  oxygen  which  contains 
about  an  inch  of  water  in  the  bottom.  Describe  the  results.  Do  you 
see  anything  falling  to  the  bottom  of  the  bottle?  A  knife-blade  or 
watch-spring  may  be  thus  burned,  by  first  drawing  the  temper  and 
using  a  larger  amount  of  kindling  material. 


50 


MODERN  CHEMISTRY 


EXPERIMENT  33.  —  Put  into  a  deflagrating  spoon  a  little  red  phos- 
phorus, ignite  it,  and  thrust  it  into  a  large  jar  of  oxygen.  Describe 
the  combustion  and  the  fumes  that  fill  the  jar.  These  are  phosphorus 
pentoxide,  a  substance  mentioned  under  deliquescent  bodies. 

6.  The  Chemical  Action.  —  In  preparing  oxygen  as  above, 
the  manganese  dioxide  remains  unchanged.  This  and 
other  facts  shown  in  the  equation  below  will  be  proved 
in  Exp.  34.  What  has  really  taken  place  is  the  same  as 
in  the  use  of  the  mercuric  oxide.  The  heat  has  simply 
decomposed  the  molecules  of  potassium  chlorate,  setting 
free  the  oxygen  and  leaving  behind  a  new  compound  con- 
taining only  potassium  and  chlorine,  called  potassium 
chloride.  The  change  may  be  shown  thus  :  — 


+  HEAT  = 


The  two  molecules  of  potassium  chlorate  shown  here 
have  each  given  up  three  atoms  of  oxygen,  which  have 
combined  to  form  three  molecules  of  oxygen,  while  two 
molecules  of  potassium  chloride  remain  behind.  These 
facts  are  more  usually  written  thus :  — 

2  KC1O3  +  heat  =  2  KC1  +  3  O2. 

7.  Effect  of  the  Manganese  Dioxide.  —  If  potassium 
chlorate  be  used  alone,  instead  of  mixing  with  manganese 
dioxide,  as  we  did  above,  the  same  results  are  obtained. 


OXYGEN,   COMBUSTION,   OZONE  51 

but  considerably  more  heat  is  required.  Apparently, 
therefore,  manganese  dioxide  has  simply  acted  by  its 
presence,  or,  as  it  is  called,  by  catalysis.  It  is  believed, 
however,  that  the  dioxide  is  first  converted  into  another 
compound,  which  at  the  temperature  present  is  unstable, 
and  that  this  in  breaking  up  yields  oxygen  and  the  dioxide 
again. 

EXPERIMENT  34.  —  To  prove  that  the  manganese  dioxide  remains 
unchanged  and  that  potassium  chloride  is  formed.  To  the  residue  in 
the  flask  in  Experiment  28,  add  about  50  cc.  of  water,  let  it  stand  a 
few  minutes,  shaking  occasionally,  warm  gently  and  then  filter.  Boil 
this  clear  filtrate  to  dryness  in  an  evaporating  dish.  While  this  is 
proceeding,  add  a  little  water  to  the  black  residue  on  the  filter  paper 
once  or  twice  to  wash  it,  throw  the  water  away,  and  let  the  black 
residue  dry.  When  the  solution  in  the  evaporating  dish  is  perfectly 
dry,  scrape  it  out,  mix  with  a  little  fresh  manganese  dioxide,  transfer 
to  a  test-tube,  and  heat.  Do  you  observe  any  indication  of  oxygen 
being  given  off?  If  not,  we  may  conclude  under  the  present  circum- 
stances that  the  oxygen  was  all  removed  in  the  previous  heating,  and 
that  the  white  solid  residue  is  KC1,  potassium  chloride,  and  not  potas- 
sium chlorate,  KC1O3. 

When  the  black  residue  on  the  filter  paper  is  dry,  mix  with  it  a 
little  potassium  chlorate,  transfer  to  a  test-tube  and  heat.  Is  oxygen 
given  off  readily  ?  What  proof  ?  Is  there  any  reason  for  believing 
that  the  black  residue  is  still  manganese  dioxide? 

8.  The  Proof  by  Weighing.  —  It  will  be  well  to  try  an 
experiment  by  which  the  facts  discovered  in  preceding 
experiments  may  be  proved.  Such  is  the  following  experi- 
ment. 

EXPERIMENT  35.  —  Put  into  a  test-tube  or  flask  about  a  gram  of 
potassium  chlorate,  put  it  upon  the  scales  and  balance  it  with  shot  or 
sand  in  a  small  box.  Now  add  about  a  half  gram  of  manganese 
dioxide,  and  then  weigh  carefully.  As  the  box  and  shot  counter- 
balance the  flask  and  potassium  chlorate,  the  weights  added  show  at 
once  the  amount  of  dioxide  used.  Now  connect  a  delivery  tube  and 
.heat  to  drive  off  the  oxygen.  When  the  operation  is  complete,  known 


52  MODERN  CHEMISTRY 

by  the  fact  that  the  gas  no  longer  bubbles  up  through  the  water,  re- 
move the  delivery  tube  from  the  water,  and  let  the  flask  cool.  When 
cold,  add  a  few  cubic  centimeters  of  water  to  dissolve  the  potassium 
chloride,  then  filter  and  wash  the  black  residue  as  before.  When 
thoroughly  dry,  weigh  the  residue  and  filter  paper  and  subtract  the 
weight  of  the  paper.  The  latter  may  be  obtained  by  weighing  ten  of 
them,  or,  if  the  balance  is  not  very  delicate,  a  hundred,  and  then  tak- 
ing the  fractional  part.  Does  the  weight  of  the  black  compound  now 
agree  with  its  weight  before  heating? 

9.  Commercial  Methods  of  making  Oxygen.  —  Most   of 
these  methods  consist  in  abstracting  oxygen  from  the  air 
by  using  a  substance  which  when  heated  or  when  under 
pressure  will  absorb  oxygen,  and  then  when  cooled  or 
when  the  pressure  is  removed  will  again  give  it  up.     One 
of  the  best  known  of  these  methods  is  Erin's,  which  con- 
sists in  using  barium  oxide,  BaO,  as  the  chemical  agent. 
When  gently  heated  in  the  air,  it  takes  up  an  additional 
amount  of  oxygen,  forming  barium  dioxide,  BaO2,  thus,  — 

BaO  +  O  =  BaO2. 

If,  now,  the  heat  is  increased,  the  barium  dioxide  is  unable 
to  retain  the  additional  atom  of  oxygen  taken  from  the 
air  and  gives  it  up  again,  thus,  — 

BaO2  +  heat  =  BaO  +  O. 

Or,  if  the  pressure  under  which  the  barium  dioxide  was 
formed  is  decreased,  the  same  results  follow  at  considera- 
bly less  expense. 

10.  Motay's  Method.  —  The  principle  of  this  is  about 
the  same  as  that  of  Brin's,  but  different  substances  are 
used.     Manganese  dioxide  and  caustic  soda,  when  heated 
moderately  in  a  current  of  air,  form  a  compound  which 
at  a  higher  temperature  is  again  decomposed,  yielding  up 
the  oxygen  previously  taken  from  the  air. 


OXYGEN,   COMBUSTION,   OZONE 


53 


11.  Other  Methods.  —  These  are  not  important  as  a 
means  of  producing  oxygen  for  commercial  or  experimental 
purposes,  but  the  principle  underlying  them  is  involved 
in  a  number  of  the  processes  of  chemistry  with  which  we 
shall  deal  later,  and  should  consequently  be  understood. 
It  will  be  noticed  that  in  all  the  methods  of  preparing 
oxygen  used  above,  we  have  employed  substances  con- 
taining a  large  per  cent  of  that  element.  There  are  sev- 
eral other  substances  of  similar  composition  which  may 
be  made  to  furnish  oxygen.  Thus,  manganese  dioxide, 
MnO2,  potassium  dichromate,  K2Cr2O7,  and  potassium 
permanganate,  KMnO4,  when  heated  with  sulphuric  acid, 
H2SO4,  will  yield  oxygen. 

EXPERIMENT  36. — Put  a  half  gram  of  manganese  dioxide  into  a 
test-tube  and  add  about  a  cubic  centimeter  of  sulphuric  acid.  Warm 
gently,  collect  a  small  bottle  of  the  gas,  and  make  the  usual  test  for 
oxygen.  What  are  the  results  ? 

It  will  be  found  that  the  dichromate  and  the  permanga- 
nate act  in  a  similar  way,  except  that  the  quantity  of  gas 
obtained  is  considerably  greater.  The  chemical  action 
may  be  shown  thus :  - 

Mn02  +  H2S04  =  MnS04  +  H2O  +  O. 


54  MODERN  CHEMISTRY 

In  a  similar  way  the  reaction  of  potassium  dicliroraate 
and  sulphuric  acid  upon  each  other  may  be  shown  ; 

K2Cr207  +  4  H2S04 

=  K2S04  +  Cr2(S04)3  +  4  H2O  +  3  O, 

and  of  potassium  permanganate  and  sulphuric  acid, 

2  KMnO4  +  3  H2SO4 

=  K2SO4  +  2  MnSO4  +  3  H2O  +  5  O. 

See  pages  322,  325,  for  application  of  this  property  of  the 
above  substances. 

12.  Characteristics  of  Oxygen.  —  Oxygen  is  an  odorless, 
colorless  gas,  a  little  heavier  than  air,  the  weight  of  a  liter 
being  1.43  g.     As  already  noted  it  is  slightly  soluble  in 
water,  and  upon  this  fact  depends  the  life  of  aquatic  ani- 
mals, which  abstract  this  free  oxygen  from  the  water.     It 
may  be  liquefied  by  extreme  cold  and  pressure.     This  was 
first  accomplished  about  a  quarter  of  a  century  ago  by 
Cailletet  and  Pictet,  who  succeeded  in  preparing  a  small 
quantity  at  great  cost.     At  present  it  is  made  in  almost 
any  amount  by  first  liquefying  air  and  then  allowing  the 
nitrogen  to  boil  out.     (See  page  100.) 

13.  Peculiarities  of  Liquid  Oxygen.  —  In  the  liquid  con- 
dition oxygen  is  of  a  pale  blue  color  and  boils  at  about 
—  180°  C.,  a  few  degrees  higher  than  the  boiling  point  of 
nitrogen.     It  presents  many  striking  peculiarities ;  a  rod 
of  carbon  heated  red  hot  and  plunged  into  the  liquid 
oxygen  at  a  temperature  180°  below  zero  burns  vigorously, 
while  a  stout  iron  wire  similarly  heated  is  rapidly  con- 
sumed with  a  brilliant  display  of  sparks.     Cotton  rags 
saturated  with  it  and  confined  in  a  cylinder,  when  ignited, 


OXYGEN,   COMBUSTION,   OZONE  55 

explode  so  violently  as  to  burst  tubes  made  of  iron  or 
brass. 

14.  Chemical  Affinity  of  Oxygen.  —  The  strongest  chem- 
ical property  of  oxygen  is  its  affinity  for  other  substances. 
This  was  seen  in  the  rapidity  of  combustion  of  the  various 
ignited  substances  when  placed  in  .an  atmosphere  of  oxy- 
gen.    From  these   experiments  it  is  not  difficult  to  see 
what  would  be  the  results  were  the  air  undiluted  oxygen. 
The  smallest  spark  would  be  sufficient  to  start  the  fiercest 
conflagration,  while  our  stoves,  furnaces,  etc.,  would  be 
rapidly  consumed,  accompanied  by  a  most  brilliant  display 
of  sparks. 

15.  Uses  of  Oxygen. — As   is  well  known,  oxygen  is 
absolutely  necessary  for  life.     It  is  absorbed  by  the  blood 
through  the  walls  of  the  air-cells  of  the  lungs  and  carried 
by  the  red  corpuscles  to  all  parts  of  the  body.     Here  it 
unites   with   the   waste   material,    burning   it   to   carbon 
dioxide  and  other  compounds,  and  at  the  same  time  warm- 
ing the  body.     The  carbon  dioxide  is  carried  back  to  the 
lungs,  from  which  it  is  thrown  off  into  the  air.     In  cases 
of  asphyxiation  pure  oxygen  is  sometimes  used  as  a  restora- 
tive, but  ordinarily,  if  breathed  for  any  length  of  time,  the 
temperature  of  the  body  rises  owing  to  the  increased  de- 
struction and  consumption  of  tissue,  and  general  feverish 
symptoms  follow.     A  limited  number  of  experiments  by 
the  author  show  that  small  animals,  such  as  mice,  when 
placed  in  an  atmosphere  of  pure  oxygen  soon  exhibit  great 
activity,  followed  by  apparent  relaxation  and  complete 
exhaustion.     Experiments  have  also  shown  that  animals 
in  oxygen  under  pressure  would  very  quickly  die,  as  if  the 
gas  in  this  condition  were  an  active  poison. 

EXPERIMENT  37.  —  Into  a  flask,  0,  the  weight  of  which  is  known, 
supported  in  a  ring-stand  as  shown  in  Fig.  13,  put  2.5  g.  of  potassium 


56 


MODERN  CHEMISTEY 


chlorate.  Let  the  tube,  d,  just  reach  through  the  cork  of  A,  nearly 
filled  with  water.  Make  e  in  two  parts,  joined  at  a  by  several  inches 
of  rubber  tubing.  By  suction  fill  e  with  water,  and  put  pinch  clamp 
upon  the  rubber.  Make  the  corks  air-tight.  With  the  tube  in  posi- 
tion, fill  B  to  the  same  height  as  water  in  .4,  open  clamp  an  instant, 


Fio.  13.  —  Apparatus  to  use  in  finding  the  Weight  of  Oxygen. 

then  empty  B.  Remove  the  clarnp  and  heat,  carefully  at  first,  until 
water  is  no  longer  forced  into  B.  When  0  is  cool,  raise  or  lower  B 
till  water  stands  at  same  height  in  both  bottles,  fasten  clamp  and 
measure  water  in  B.  This  equals  volume  of  oxygen  at  pressure  and 
temperature  of  the  room.  Reduce  to  standard  conditions.  (See 
p.  96.)  Weigh  0;  loss  equals  weight  of  oxygen  expelled.  Knowing 
the  weight  of  a  certain  number  of  cubic  centimeters,  find  weight  of 
one  liter. 

By  similar  methods,  the  weight  of  a  liter  of  various 
other  gases,  insoluble  in  water,  may  also  be  determined. 

16.  Oxidation  and  Combustion.  —  When  any  substance 
combines  with  oxygen  to  form  a  new  compound,  it  is  said 
to  be  oxidized,  and  the  process  is  known  as  oxidation. 
This  may  be  slow  or  rapid.  When  it  takes  place  so 
rapidly  as  to  be  accompanied  by  heat  and  light,  the  pro- 
cess is  called  combustion.  To  illustrate  :  when  a  piece  of 
iron  is  exposed  to  the  air  in  the  presence  of  moisture,  it 
soon  becomes  covered  with  rust,  which  is  really  an  oxide  of 


OXYGEN,   COMBUSTION,   OZONE 


57 


iron;  in  other  words,  the  iron  has  been  oxidized.  Again, 
when  we  tipped  the  iron  wires  with  sulphur  and  ignited 
it,  they  were  rapidly  consumed  in  the  jar  of  oxygen  with 
much  heat  and  considerable  light.  This  was  combustion. 
A  pile  of  brush  will  gradually  decay,  or  oxidize,  without 
any  perceptible  heat,  but  by  setting  it  on  fire  we  quickly 
destroy  it  by  the  process  of  combustion. 

^t.  Combustible  Substances  and  Supporters  of  Combus- 
tion.—  Substances  which  thus  burn  in  oxygen  or  its 
diluted  form,  the  air,  are  said  to  be  combustible,  while  the 
substance  in  which  they  burn  is  called  a  supporter  of  com- 
bustion. Thus,  when  a  jet  of  hydrogen  burns  in  a  jar  of 
oxygen,  the  former  would  be 
spoken  of  as  the  combustible 
substance,  and  the  latter  as 
the  supporter  of  combustion. 
It  is  true,  however,  that  if  we 
thrust  a  delivery  tube  from 
which  a  current  of  oxygen  is 
issuing,  up  into  a  jar  of 
hydrogen  which  is  burning  at 
the  mouth,  as  seen  in  Fig.  14, 
the  jet  of  oxygen  will  be  seen  to  burn  in  the  atmosphere 
of  hydrogen,  just  as  before  the  hydrogen  did  in  the  oxy- 
gen. Yet  in  view  of  all  the  facts  it  seems  better  to  adhere 
to  the  statement  previously  made,  that  it  is  really  the 
hydrogen  which  burns,  and  the  oxygen  which  supports 
tl^e  combustion. 

18.  Kindling  Temperature.  —  It  is  well  known  that  some 
substances  ignite  much  more  readily  than  others.  This, 
chemically  speaking,  simply  means  that  some  combine 
with  oxygen  at  a  lower  temperature,  or  much  more  readily, 
than  do  others.  Thus,  substances  like  alcohol  and  many 


FIG.  14. 


58  MODERN  CHEMISTRY 

oils  need  but  little  heat  to  ignite  them;  phosphorus,  like- 
wise. Pine  wood  needs  a  higher  temperature,  and  hard 
wood  still  higher.  The  point  at  which  any  substance 
takes  fire  is  said  to  be  its  kindling  temperature. 

19.  What  is  a  Flame  ?  —  A  flame  is  simply  burning  gas. 
Whenever  a  substance  will  not  burn  with  a  flame,  it  is 
because  there  is  either  no  gas  present  or  there  is  nothing 
which  may  be  converted  into  a  gas.  For  example,  when 
a  lamp  burns,  the  oil  drawn  up  through  the  wick  by  capil- 
lary attraction  is  volatilized  by  the  heat,  and  it  is  the 
burning  of  this  gas  that  makes  the  flame.  On  the  other 
hand,  charcoal  and  the  hardest  natural  coals  do  not  burn 
with  a  flame,  because  previous  heating  has  driven  out  all 
the  gaseous  products.  However,  they  may  be  heated  suf- 
ficiently to  be  partially  converted  into  carbon  monoxide, 
a,gas  which  burns  with  a  pale  blue  flame. 

^0.  The  Oxy-hydrogen  Blowpipe.  —  This  is  a  lamp 
arranged  for  burning  hydrogen  thoroughly  mixed  with 
oxygen,  and  affords  one  of  the  hottest  flames  known. 

Its  construction  will  be  understood 
from  the  figure,  which  gives  a 
sectional  view.  The  inner  tube, 
m,  is  connected  with  the  oxygen 
tank,  and  the  outer,  n,  with  the 
hydrogen.  In  this  way,  as  the 
inner  tube  is  somewhat  shorter, 
the  gases  become  thoroughly  mixed 
before  leaving  the  tube  at  JEJ,  hence 
the  combustion  is  perfect.  The 
FIG.  is.  —  The  Oxy-hydro-  pressure  should  be  so  regulated 

gen  Blowpipe.  .  .  111 

as  to  furnish  twice  as  much  hydro- 
gen by  volume  as  oxygen.  This  blowpipe  is  used  for 
melting  very  refractory  substances.  It  is  also  used  espe- 


OXYGEN,   COMBUSTION,    OZONE  59 

cially  in  furnishing  light  for  stage  effects,  stereopticon 
views,  and  for  illuminating  moving  floats  in  street  parades 
given  after  dark.  When  used  for  these  purposes  the 
almost  non-luminous  blue  flame  is  allowed  to  strike  upon 
a  stick  of  prepared  lime  supported  in  a  socket  just  in 
front  of  the  blowpipe.  This  is  often  called  the  calcium 
or  Drummond  light,  and  is  of  dazzling  whiteness,  rivaling 
the  electric  arc  light. 

OZONE 

21.  Its  Discovery.  —  This  substance,  on  account  of  its 
peculiar  odor,  was  named  from  a  Greek  word  which  means 
to  smell.     It  was  first  observed  in  passing  electrical  sparks 
through  a  tube  of  oxygen,  and  is  always  noticeable  when 
an  electric  discharge  takes  place  in  the  air. 

22.  What  is  Ozone  ? — For  some  time  it  was  regarded  as 
a  compound  body,  but  is  now  known  to  be  simply  a  con- 
densed form  of  oxygen.     Quite  a  number  of  substances, 
such  as  sulphur  and  phosphorus,  appear  in  a  form  other 
than  the  usual  one  :  this  is  known  as  the  allotropic,  a  word 
which  means  simply  another  form. 

23.  Methods  of  obtaining  Ozone.  —  It  is  impossible  to 
prepare  ozone  in  large  quantities  in  a  pure  condition,  be- 
cause by  the  best  methods  only  a  small  per  cent  of  the 
oxygen  used  is  converted  into  its  allotropic  form.     Usu- 
ally not  over  one  or  two  per  cent  is  obtained,  and  under 
the  most  favorable  circumstances  only  about  twenty  per 
cent.     In  the  ordinary  methods  of  making  oxygen,  ozone 
is  almost  always  obtained  in  appreciable  quantities.     One 
of  the  easiest  methods  of  preparing  it  is  given  in  the  fol- 
lowing :  — 

EXPERIMENT  38.  —  Scrape  a  stick  of  phosphorus  perfectly  clean, 
put  it  into  a  bottle,  and  add  water  sufficient  to  cover  about  half  of  it. 
In  a  few  minutes  the  presence  of  ozone  may  be  detected  by  suspending 


60  MODERN   CHEMISTRY 

in  the  bottle  a  strip  of  white  paper  moistened  with  a  solution  of 
potassium  iodide  and  starch.  The  paper  will  turn  decidedly  blue.  A 
solution  of  potassium  permanganate  treated  with  strong  sulphuric 
acid  also  gives  the  test  for  ozone,  along  with  the  oxygen  thus 
evolved. 

24.  Ozone  in  the  Air.  —  Ozone  is  believed  to  exist  in 
appreciable  quantities  in  the  atmosphere,  being  produced 
mainly  by  electrical  discharges.      Its  presence  in  dwell- 
ings is  never  perceptible,  and  scarcely  ever  in  large  cities, 
but  in  the  country  a  strip  of  starch  paper  exposed  to  the 
breeze  for  some  time  shows  the  characteristic  blue  color. 

25.  How  Ozone  differs  from  Oxygen.  —  As  already  stated, 
it  is  a  condensed  form  of  oxygen.     Experiment  has  shown 
that  if  a  given  amount  of  ozone  is  decomposed  so  as  to 
form  ordinary  oxygen,  the  volume  increases  one-half ;  that 
is,  100  cc.  of  ozone  would  become  150  cc.  of  oxygen.     On 
the  other  hand,  if  a  closed  volume  of  oxygen  be  subjected 
to  a  silent  discharge  of  electricity  so  as  to  convert  a  por- 
tion of  it  into  ozone,  a  corresponding  decrease  of  volume 
takes  place. 

26.  For   example,  suppose  150  cc.  of  oxygen  be  thus 
treated,  and  that  30  cc.  are  converted  into  ozone.     It  is 

found  that  by  absorbing  this  ozone 
so  as  to  separate  it  from  the  remain- 
ing oxygen,  and  again  setting  it 
free,  there  are  only  20  cc.  of  ozone, 
Molecule  of  Molecule  of  wnile  but  120  cc.  of  oxygen  remain. 

Oxygen.  Ozone.  * 

If,  however,  this  20  cc.  of  ozone  be 

heated  strongly,  so  as  to  convert  it  into  oxygen  again, 
we  shall  find  the  volume  increases  to  30  cc.  The  mole- 
cule of  ozone  therefore  would  differ  from  that  of  oxygen, 
in  that  it  contains  three  atoms  of  oxygen,  while  the  other 
has  only  two.  This  is  shown  in  the  accompanying  figure. 


OXYGEN,   COMBUSTION,   OZONE  61 

From  this  it  naturally  follows  that  ozone  is  50%  more 
dense  than  oxygen. 

27.  Properties  of  Ozone.  —  The  properties  are  also  dif- 
ferent from  those  of  oxygen.     Its  odor  has  already  been 
mentioned.     If  placed  in  a  long  glass  tube,  so  as  to  give 
considerable  depth,  it  is  seen  to  have  a  blue  tinge.     It 
readily  destroys  the  color  of  such  vegetable  solutions  as 
indigo  and  litmus  and  quickly  attacks  such  metals  as  mer- 
cury and  silver,  which  remain  unchanged  in  the  air  and 
which  are  little  affected  by  oxygen  when  heated.     We 
have  seen  its  effect  upon  potassium  iodide  above.     Free 
iodine  always  turns  starch  blue.     In  the  test  made,  the 
ozone  united  with  the  potassium  in  the  potassium  iodide  to 
form  an  oxide  with  the  metal,  and  the  iodine  was  thus  set 
free.     In  the  same  way  if  a  drop  of  ammonium  hydroxide 
be  let  fall  into  a  jar  of  ozone,  a  dense  white  cloud  forms, 
owing  to  the  fact  that  a  white  solid  compound  of  ammonia 
is  formed,  thus  :  — 

2  NH4OH  +  O3  ==  NH4NO2  +  3  H2O. 

28.  Liquid  Ozone.  —  Ozone  may  be  liquefied  at  ordinary 
atmospheric    pressure    by  reducing   the   temperature   to 
—  106°  C.,  — a  point  considerably  higher  than  that  at  which 
oxygen  liquefies.     Ozone  is  also  a  very  unstable  body, 
changing  back  readily  into  oxygen ;  an  illustration  of  this 
is  seen  in  the  fact  that  if  a  quantity  of  ozone  be  suddenly 
compressed  and  heated,  it  explodes  with  violence.     It  is 
because  of  this  instability  that  ozone  is  so  strong  an  oxi- 
dizing agent.     The  nascent  oxygen  liberated,  if  inhaled, 
attacks  the  mucous  linings,  causing  an  irritation  some- 
what like  that  of  dilute  chlorine.     More  than  this,  head- 
ache soon  follows,  if  much  ozone  is  inhaled,  even  though 
diluted  with  considerable  quantities  of  oxygen. 


62  MODERN  CHEMISTRY 

TABULAR  VIEW   OF   DIFFERENCES 


OXYGEN 


Colorless. 
Odorless. 
Density;  slightly  heavier 

than  air. 

Two  atoms  in  molecule. 
Strong  oxidizer. 
Liquefies  at  -  180°C. 
Stable. 


OZONE 


Blue. 

Peculiar  odor. 

Density;    considerably 

heavier  than  air. 
Three  atoms  in  molecule. 
Very  strong  oxidizer. 
Liquefies  at  -  106°  C. 
Unstable. 


29.  Value  of  Ozone.  —  It  is  believed  to  have  a  beneficial 
effect  in  destroying  disease  germs  and  in  oxidizing  decay- 
ing organic  matter. 

^^80.  Isomeric  and  Polymeric  Bodies.  —  Just  as  ozone  is 
another  form  of  oxygen,  so  we  shall  find  that  phosphorus 
and  certain  other  elements  present  allotropic  forms  as 
unlike  the  usual  forms  as  oxygen  and  ozone.  When  we 
come  to  the  study  of  compound  bodies  we  often  find 
two  substances  not  at  all  alike  in  properties,  which,  upon 
analysis,  are  found  to  contain  exactly  the  same  elements 
united  in  exactly  the  same  ratios.  Thus  aldehyde  and 
oxide  of  ethylene  both  have  the  same  -composition,  repre- 
sented by  the  formula  C2H4O,  but  their  properties  are 
very  different.  Such  substances  are  said  to  be  isomeric. 

31.  Sometimes  while  they  have  the  same  percentage 
composition,  the  vapor  density  of  one  will  be  several 
times  that  of  the  other.  Thus  acetylene  is  C2H2,  and 
benzine  C6H6.  In  each  case  the  carbon  is  ^|,  or  92.3  per 
cent,  of  the  molecule  ;  but  the  molecular  weight  of  one 


OXYGEN,   COMBUSTION,   OZONE  63 

is  three  times  that  of   the   other.     Such  substances  are 
said  to  be  polymeric. 

HYDROGEN  DIOXIDE:  H202 

32.  Composition.  —  This  is  a  compound  which  in  some 
of  its  characteristics  resembles  ozone.     In  composition  it 
is  most  like  water,  having  one  additional  atom  of  oxygen. 
It  is  believed  to  exist  in  the  air  in  minute  quantities,  and 
some  of  the  effects  attributed  to  ozone  may  be  due  to 
hydrogen  dioxide. 

33.  How  to.  obtain  It.  —  For  experimental  purposes  it  is 
usually  prepared  by  treating  barium  dioxide  with  dilute 
sulphuric  or  hydrochloric  acid. 

EXPERIMENT  39.  —  Add  to  about  a  gram  of  barium  dioxide  a  little 
water,  and  then  dilute  sulphuric  or  hydrochloric  acid.  Stir  for  a 
moment  or  two  with  a  glass  rod. 

To  prove  the  presence  of  hydrogen  dioxide,  add  a  few  drops  of 
potassium  dichromate  and  about  a  half  cubfc  centimeter  of  ether,  and 
shake  well.  The  hydrogen  dioxide  forms  a  blue  solution  with  the 
dichromate,  which  is  taken  up  by  the  ether  and  thus  concentrated 
within  little  space. 

34.  Some  of  its  Peculiarities.  —  Like  water,  it  is  a  color- 
less  liquid,  but   is   thicker  or    sirupy,   and   has  a  bitter 
taste.     It  is  very  unstable,  decomposing  at  all  tempera- 
tures into  water   and   oxygen  ;    it   is   therefore    a   good 
bleaching  agent,  the  bleaching  being  done  by  the  nascent 
oxygen.     Like  ozone,  it  readily  tarnishes  silver  and  decom- 
poses potassium  iodide,  giving  in  the  same  way  a  test 
with   starch   paper.      It   is   soluble   in   water,    and   thus 
diluted  it  will  bleach  the  skin,  but  when  concentrated  it 
burns  or  blisters  it. 

35.  Uses. — This  compound,  more  usually  sold  under 
the  name  hydrogen  peroxide,  is  now  manufactured  very 


64  MODEEN  CHEMISTRY 

cheaply,  and  is  used  to  a  considerable  extent  as  a  bleach- 
ing agent,  especially  for  hair  and  feathers.  It  is  used 
largely  by  dentists  and  in  surgery  as  an  antiseptic,  and  to 
some  extent  in  cleansing  oil  paintings  and  engravings. 

SUMMARY  OF   CHAPTER 

Discovery  of  oxygen. 

Meaning  of  term. 

Abundance  of  oxygen  —  Various  forms  in  which  it  occurs. 
Methods  of  preparing  oxygen. 
Priestley's  method. 
Ordinary  method. 

Chemicals  and  apparatus  used . 
Chemical  changes  involved. 

Proof  of  these  changes  —  Experimental. 
Proof  by  weight. 
Other  methods. 

Character  of  substances  used. 

Characteristics  of  oxygen  —  Compare  with  hydrogen  in 
Color,  odor,  density,  combustibility. 
Power  of  supporting  combustion. 
How  would  you  distinguish  the  two  ? 
Some  peculiarities  of  liquid  oxygen. 
Uses  of  oxygen. 
Special. 

Meaning  of  terms  combustion,  oxidation,  flame,  kindling  point. 

Illustration  of  the  terms. 

Description  and  drawing  of  oxyhydrogen  blowpipe. 

Uses  for  it. 
Ozone  —  Meaning  of  the  word. 

What  is  its  relation  to  oxygen  ? 
Methods  of  obtaining. 
Compare  with  oxygen,  showing  differences. 
Value  of  ozone. 
Hydrogen  dioxide  —  Formula. 

Compare  with  water  in  properties. 
Uses  for  the  compound. 


CHAPTER  VI 

CHEMICAL  NOTATION,   SYMBOLS,  FORMULA,  EQUATIONS, 
PROBLEMS 

1.  Symbols.  —  The  student  will  have  noticed  that  in 
chemistry  we  frequently  employ  a  short-hand  method  of 
expressing  the  different  elements  and  their  compounds. 
Thus  we  have  seen  that  hydrogen  is  represented  by  H, 
oxygen  by  O,  and  so  on.     These  are  called  symbols. 

2.  Their  Form.  —  Frequently,  the  symbol  of  an  element 
is  its  initial  letter ;  often,  however,  this  is  the  same  for  a 
number  of  elements,  as  for  example,  carbon,  calcium,  cad- 
mium,   copper,    etc.      In   such   cases,  the   most   common 
usually  is  designated  by  the  initial  letter;  another  by  the 
first  and  second  letter,  as  Ca,  calcium;  another  by  the  first 
and   some   other  distinctive  letter,  as  Cd  for  cadmium. 
Frequently,  the  first  or  the  first  and  second  letters  of  the 
Latin  term  for  the  same  substance  are  used,  as  Cu  for 
copper,  from  cuprum.     In  lixe  manner,  sulphur,  silicon, 
selenium,  silver,  are  designated  by  the  symbols  S,  Si,  Se, 
and  Ag  (from  the  Latin  argentuni).     The  Latin  has  fur- 
nished a  number  of  the  symbols  of  the  common  elements : 
thus,  sodium,  Na  (natrium),  potassium,  K  (kalium),  iron, 
Fe  (ferrum).     The  symbol,  Hg  (hydrargyrum),  for  mer- 
cury is  from  the  Greek. 

3.  Strict  Meaning.  —  Strictly  speaking,  the  symbol  of 
an  element  not  only  represents  that  element,  but  a  defi- 
nite amount  of  it ;  that  is,  one  atom.     Hence,  to  speak  of 
an  element  by  using  its  symbol  when  we  mean  an  indefinite 
amount  is  unscientific  and  should  not  be  practiced. 

65 


66  MODERN  CHEMISTRY 

4.  Formulae.  —  As   the    elements    are    represented   by 
symbols,  so  compound  bodies  are  by  formulae  ;  that  is,  i>y 
an    aggregation    of    symbols.       Compounds    are    usually 
named  by  simply  combining  the  terms  representing  the 
elements  entering  into  the  composition,  the  more  electro- 
positive being  placed  first ;  thus,  potassium  iodide  consists 
of  two  elements,  potassium  and  iodine.     The  formulae  are 
always  arranged  in  the  same  way:   thus,  KI,  potassium 
iodide ;  KC1,  potassium  chloride.     It  will  be  seen,  there- 
fore, that  as  a  symbol  represents  an  atom  of  an  element, 
so  a  formula  represents  the  smallest  amount  of  a  compound 
body,  a  molecule. 

5.  Sub-figures.  —  When  the  elements  enter  into  com- 
position, in  other  than  a  single  atom  of  each,  that  fact  is 
indicated  by  putting  a  small  figure  below  and  at  the  right 
of  the  symbol ;   thus,  H2O,  the  formula  for  water,  indi- 
cates that  there  are  two  atoms  of  hydrogen  in  the  mole- 
cule, and,  H2O2,   for   hydrogen  peroxide,  indicates  that 
there  are  two  atoms  of  each.     These  sub-figures  are  some- 
times appended  to  a  group  of  elements,  in  which  case  the 
group  is  inclosed  in  parentheses  and  the  figure  placed 
outside  ;  for  example,  lime-water,  or  calcium  hydroxide  is 
Ca(OH)2.     This  might  also  be  written  CaO2H2,  but  the 
former  method  is  preferable,  as  will  be  seen  later.     If  we 
desire  to  indicate  more  than  one  molecule  of  a  substance, 
this  is  done  by  prefixing  a  coefficient   to   the   formula. 
Thus,  2  HC1  indicates  two  molecules  of  hydrochloric  acid  ; 
5  H2O,  five  molecules  of  water. 

6.  Radicals.  —  By  a  radical  we  mean  a  group  of  ele- 
ments which  in  most  chemical   reactions   seem  to   hold 
together,  but  which  do  not  by  themselves  form  a  distinc- 
tive compound.     For  example,  (HO)  seen  in  the  formula 
for  lime-water  is  a  radical  known  as  hydroxyl,  which  enters 


REACTIONS  67 

into  a  great  many  compounds.  Again,  (NH4)  is  a  group 
called  ammonium,  which  is  very  common,  and  ordinary 
ammonia  water  is  NH4OH,  composed  of  two  radicals 
(NH4)  and  (OH),  not  written  NH5O,  because  of  this  fact. 

7.  Reactions.  —  Equations   in    chemistry    which    show 
the  chemical  changes  that  take  place  when  two  or  more 
substances  react  with  each  other  are  called  reactions.     We 
have  already  seen  a  number  of  these  ;  thus  :  — 

2  Na  +  2  H2O  =  2  NaOH  +  H2; 
Zn  +  H2SO4  =    ZnSO4   +  H2. 

8.  The  first  indicates  that  two  atoms  of  sodium  uniting 
with  two  molecules  of  water  will  produce  two  molecules 
of  caustic  soda  and  two  atoms  or  one  molecule  of  hydro- 
gen.     Another  thing  must  be  noticed,  and  that  is  that 
every  atom  appearing  in  one  member  of  the  equation  must 
also  be  found  in  the   other.      Thus,  the  two  atoms  of 
sodium  are  seen  in  the  second  member  of  the  equation  in 
the  two  molecules  of  caustic  soda,  the  four  atoms  of  hydro- 
gen in  the  water  appear  partly  in  the  caustic  soda  and 
partly  as  free  hydrogen;  likewise  the  two  atoms  of  oxy- 
gen in  the  water  are  found  in  the  caustic  soda.     It  must 
be  borne  in  mind  that  a  coefficient  before  a  formula  mul- 
tiplies every  symbol  in  that  formula.     Thus, 

2  KC1O3  means  that  there  are  two  atoms  of 
potassium,  K;  two  of  chlorine,  Cl;  and  six 
of  oxygen.  This  will  be  seen  from  the  fol- 
lowing illustration  :  — 

a  represents  a  molecule  of  water  containing  two 
atoms  of  hydrogen  and  one  of  oxygen ;  b  represents 
a  second  molecule  having  the  same  composition.     Tak- 
ing both  together,  or  two  molecules  of  water,  2  H2O,  we  see  there  are 
four  atoms  of  hydrogen  and  two  of  oxygen. 


68  MODERN   CHEMISTRY 

9.  Atomic  Weights.  —  We  cannot  think  of  matter  with- 
out assigning  to  it  some  weight.  So  the  atoms  of  the 
elements,  though  the  smallest  conceivable  portions  of 
matter,  are  assumed  to  have  definite  weights.  Hydrogen, 
being  the  lightest  of  substances,  is  taken  as  the  standard,* 
and  its  atomic  weight  is  assumed  to  be  one,  or  by  some, 
as  one  micro-crith.  Of  course,  a  weight  as  small  as  this 
has  never  been  determined,  and  is  therefore  merely  an 
abstract  idea ;  but  something  is  necessary  for  comparison. 
When  we  speak  of  the  atomic  weight  of  an  element,  there- 
fore, we  simply  mean  its  density  compared  with  hydro- 
gen. Thus,  we  say  the  atomic  weight  of  oxygen  is  16,  of 
carbon,  12 ;  we  mean  that  these  elements  are,  respectively, 
sixteen  and  twelve  times  as  heavy  as  hydrogen,  or,  if  one 
cubic  foot  of  hydrogen  weighs  a  gram,  one  cubic  foot  of 
oxygen  will  weigh  sixteen  grams. 

10.  Molecular  Weight.  —  By  molecular  weight  we  mean 
the  sum  of  the  weights  of  the  atoms  entering  into  the 
composition  of  the  molecule.  For  example,  H2O  repre- 
sents a  molecule  of  water  ;  the  two  atoms  of  hydrogen 
weigh  2,  the  one  of  oxygen,  16,  or  all  together,  18.  The 
molecular  weight  of  water  is  therefore  18.  Now  if  we 
examine  any  chemical  equation,  we  will  find  that  the  sum 
of  atomic  weights  in  one  member  must  equal  the  sum  of 
those  in  the  other  member.  Take  the  following  :  — 

Na  +  H2O  =  NaOH  +  H, 

and  substituting  the  atomic  weights  as  given  in  the  table 
on  page  9,  we  have 

23  +  (2  +  16)  =  (23  +  16  +  1)  +  1,  or  41  =  41  ; 
and  this  must  always  be  so  in  any  true  reaction. 

*  There  has  long  been  a  controversy  whether  Hydrogen,  H  =  1,  or 
Oxygeu,  0  =  16,  should  be  the  standard.  The  latter  is  increasing  in  favor. 


EQUATIONS  69 

11.  Writing  Equations. — A  chemical  equation  is  valu- 
able in  that  it  shows  at  once  in  concise  form  not  only  the 
substances  which   enter  into  the  reaction,  but  also  the 
products  formed,  and  the  exact  amount  of  each.     At  first 
the  student  will  experience  some  difficulty  in  completing 
even  the  simpler  reactions,  but  he  must  remember  that 
they  only  show  what  has  been  proven  by  experiment.     Thus 
on  page  82  we  decomposed  water  by  electricity  and  ob- 
tained two  gases,  one  double  the  other  in  quantity.    These 
were  shown  to  be  hydrogen  and  oxygen.     We  represent 
these  facts  by  the  reaction, 

H20  =  H2  +  O. 

When  we  treated  water  with  sodium,  we  obtained  not  only 
a  gas,  which  was  hydrogen,  but  a  solution  of  caustic  soda. 
Representing  our  experiments  in  brief  form,  we  wrote 

H2O  +  Na  =  NaOH  +  H. 

So  all  reactions  are  determined  experimentally,  and  the 
student  at  first  will  be  called  upon  to  write  but  few  which 
he  has  not  worked  out  himself. 

12.  Practical  Value  of   the  Equation.  —  Having  deter- 
mined by  experiment  the  products  that  are  formed  in  any 
chemical  reaction,  and  having  therefrom  written  the  equa- 
tion, we  can  readily  ascertain  the  amount  of  each  product 
that  will  be  formed  from  a  certain  amount  of  another ;  or 
if  required  to  produce  a  definite  quantity  of  any  body,  we 
can  calculate  what  it  will  be  necessary  to  use  in  obtaining 
it.     To  illustrate,  suppose  we  are  required  to  determine 
how  much  zinc  will  be  necessary  for  the  preparation  of 
50g.  of  hydrogen.     We  would  first  write  the  equation, 
showing  the  preparation  of  hydrogen :  — 

Zn  +  H2S04  =  H2  +  ZnS04. 


70  MODERN  CHEMISTRY 

In  the  table  we  find  the  atomic  weight  of  zinc  is  65 ; 
looking  at  the  reaction,  then,  we  would  see  that  65  parts 
of  zhic  by  weight  produce,  when  reacting  with  the  acid, 
2  parts  of  hydrogen.  The  gas  obtained  is  therefore  fa  by 
weight  of  the  metal  used. 

Then,    50g.  =  -6V 

gL  =  i  of  50  g.  =  25  g. 

||  =  65  x  25  g.  =  1625  g.  of  Zn. 

PROBLEM  1 .  —  How  much  sulphuric  acid  is  it  necessary  to  put  with 
260  g.  of  zinc  in  preparing  hydrogen? 

Using  the  same  reaction  as  above,  we  find  first  the  molecular  weight 
of  H2SO4,  which  is  98.  We  see  then  that  65  parts  of  zinc  unite  with 
98  of  acid,  or  the  acid  used  is  |§  of  the  rnetal. 

Then,         ||  of  260  g.  Zn  =  98  x  26°  =  392  g.  H2SO4. 

65 

Some  prefer  to  solve  such  problems  by  proportion,  thus :  — 

The  wt.  of  the  Zn  :  wt.  of  acid  : :  wt.  of  Zn  in  g. :  wt.  of  acid  in  g. ; 
or,  65  :  98  : :  260  :  x. 

,=Mx2eo  =  m 

65 

PROBLEM  2.  —  In  using  260  g.  of  zinc  in  preparing  hydrogen,  how 
much  zinc  sulphate,  ZnSO4,  will  be  obtained? 

PROBLEM  3.  —  How  many  grams  of  oxygen  may  be  obtained  from 
450  grams  of  potassium  chlorate? 

PROBLEM  4.  —  How  much  caustic  soda  will  be  produced  in  prepar- 
ing 10  g.  of  hydrogen  by  using  metallic  sodium  and  water? 

SUMMARY  OF  CHAPTER 

Symbols  and  formulae  —  Difference  between  them. 
Composed  of  what. 
Exact  meaning  of  each. 


NITROGEN  AND  ITS   COMPOUNDS  71 

Radicals.       .  Atomic  and  molecular  weights. 

Meaning  of  the  term.  Meaning  of  the  terms. 

Illustrations.  Illustrations. 

Chemical  equations. 
Value  of. 
Problems. 


CHAPTER   VII 

NITROGEN  AND  ITS  COMPOUNDS 

NITROGEN  :  N  =  14 

1.  History.  —  Nitrogen,   meaning   niter  producer,   was 
given  this  name  because  of  its  being  an  important  con- 
stituent of  saltpeter,  often  called  niter.     It  had  previously 
been  called  azote,  a  term  which  meant  that  it  would  not 
support  life. 

2.  Where   found.  —  As   already  stated,   nitrogen   con- 
stitutes about  four-fifths  of  the  air,  and  is  uncombined. 
It  also  exists  in  various  compounds,  such  as  saltpeter, 
potassium   nitrate,    KNO3,   and   Chile    saltpeter,    sodium 
nitrate,  NaNO3.     It  also  enters  into  the  composition  of 
many  vegetable  and  animal  products,  and  in  their  decom- 
position is  given  off  into  the  air  in  the  form  of  ammonia, 
NH3. 

3.  How  to  prepare   Nitrogen.  —  As  nitrogen  exists  so 
abundantly  in  a  free  state  in  the  air,  this  is  the  best  source 
from  which  to  obtain  it.     Any  method  by  which  we  can 
remove  the  oxygen  and  leave  the  nitrogen  will  do.     For 
this  purpose  phosphorus  is  generally  used. 

EXPERIMENT  40.  —  Cover  a  large  flat  cork  with  a  coating  of  plaster 
of  paris  and  float  it  upon  a  pan  or  basin  of  water.  A  small  iron 
saucer  serves  well  instead  of  the  cork.  Put  upon  it  a  small  piece  of 


72 


MODERN  CHEMISTRY 


FIG.  16. 


phosphorus  and  ignite.  Quickly  place  over  the  burning  phosphorus 
a  large  wide-mouthed  jar.  Notice  that  the  water  gradually  rises  in 
the  jar  to  take  the  place  of  the  consumed  oxygen,  and  that  in  a  few 
minutes  the  white  fumes  are  absorbed  by  the  water.  Owing  to  the 
expansion  caused  by  the  heat  some  bubbles  of  air  almost  always 
escape  in  the  early  part  of  the  experiment. 

Jf  the  phosphorus  is  not  ignited,  but  the  combination  with  the 
oxygen  is  allowed  to  take  place  slowly, 
this  loss  may  be  avoided,  but  several  hours 
are  required.  Sometimes  it  is  more  con- 
venient to  use  a  deflagrating  spoon  instead 
of  a  cork ;  if  so,  the  handle  must  be  bent 
V-shaped,  so  as  to  bring  the  phosphorus 
above  the  water  even  after  it  has  risen  in 
the  jar.  Notice  about  how  much  the 
water  rises.  When  the  fumes  have  all 
disappeared,  lift  the  jar  and  put  a  burning 
candle  up  into  the  gas.  What  happens? 
Compare  it  with  similar  tests  with  oxygen  and  with  hydrogen. 

4.  Other  Ways  of  preparing  Nitrogen. — The  method 
already  given,  while  the  easiest  and  most  commonly  used, 
does  not  give  as  pure  nitrogen  as  may  be  obtained  in 
some  other  ways.  If  a  current  of  air  be  made  to  stream 
slowly  over  a  tube  con- 
taining copper  turnings  Mr 
heated  to  redness,  the  oxy- 
gen will  combine  with  the 
copper,  forming  copper  ox- 
ide, and  the  nitrogen  will 
remain.  Then  if  this  is 

allowed  to  bubble  through     FIG.  17. —Nitrogen,  prepared  bypass- 

a  bottle  of  lime-water,  the  ing  Air  over  Copper' 

carbon  dioxide  will  be  absorbed,  and  we  shall  obtain  a 
fairly  pure  nitrogen.  The  illustration  will  show  the 
method. 


NITROGEN  AND  ITS   COMPOUNDS  73 

Nitrogen  may  also  be  obtained  by  heating  certain  com- 
pounds containing  it. 

EXPERIMENT  41.  —  Into  a  small  flask  put  1  or  2  g.  of  sal  am- 
moniac, NH4C1,  and  the  same  amount  of  sodium  nitrite,  and  add 
about  30  cc.-bi_ water.  Heat  gently  and  cautiously,  and  collect  the 
gas  over  water  as  you  did  oxygen  and  hydrogen.  Test  the  gas  for 
nitrogen.  What  are  your  conclusions? 

5.  Peculiarities  of   Nitrogen.  —  From   the   experiments 
made  the  student  will  notice  that  the  gas  has  no  color ; 
it  is  odorless,  lighter  than  air,  will  neither  burn  as  does 
hydrogen,   nor  support  combustion  as  does  oxygen.      It 
has  no  affinity  for  other  substances  at  ordinary  tempera- 
tures.     It  will  combine  with  red-hot  magnesium  in  the 
absence  of   oxygen,  and  with   oxygen  when   a  discharge 
of  electricity  takes  place,  both  of  which   methods  have 
been  used  in  preparing  argon  from  its  mixture  with  atmos- 
pheric  nitrogen.      It    will    not    support    respiration   any 
more  than  it  will  combustion,  and  is  one  of  the  most  inac- 
tive substances  known.     This  inactivity,  or  feeble  chemi- 
cal affinity  of  nitrogen,  is  the  reason  for  the  instability  of 
many  of  its  compounds,  as  seen  in  the  explosiveness  of 
gunpowder  and  nitroglycerine. 

6.  Value  of  Nitrogen.  —  The  use  of  nitrogen,  except  in 
the  form  of  many  valuable  compounds,  seems  to  be  simply 
to  dilute  the  oxygen  of  the  air  as  already  stated. 

COMPOUNDS  OF  NITROGEN 

7.  In  an  indirect  way  nitrogen  forms  a  large  number 
of  compounds,  many  of  which  are  very  valuable.     Among 
these  we  shall  first  consider  ammonia. 

8.  Ammonia,  NH3.  — As  already  stated,  ammonia  is  one 
of  the  products  formed  in  the  decomposition  of  nitroge- 


74  MODERN  CHEMISTRY 

nous  organic  matter ;  that  is,  organic  matter  which  con- 
tains nitrogen  in  addition  to  the  usual  carbon,  hydrogen, 
and  oxygen.  It  finds  its  way  into  the  air  from  these 
sources,  and  being  absorbed  by  the  moisture  of  the  air  is 
brought  down  in  the  rain,  and  usually  exists  in  very  small 
quantities  in  cistern  and  river  water.  With  these  excep- 
tions, ammonia  does  not  occur  free  to  any  extent,  but  is 
found  abundantly  in  certain  compounds,  especially  sal 
ammoniac  or  ammonium  chloride,  NH4C1. 

9.  The  commercial  supply  of  ammonia  is  obtained  from 
the  distillation  of  coal  in  the  manufacture  of  common 
\lluminatinggas.  (See  page  153.)  The  decay  of  organic 
matter,  attended  by  the  formation  of  ammonia,  occurs  as 
follows :  when  the  nitrogenous  matter  decomposes,  the 
former  arrangement  existing  among  the  atoms  of  carbon, 
oxygen,  nitrogen,  and  hydrogen  is  broken  up,  and  in  the 
rearrangement  the  nitrogen  and  hydrogen  unite  to  form 
ammonia. 

10.  Ammonia  prepared  from  Coal.  —  In  the  distillation 
of  coal  the  process  is  really  the  same,  but  more  rapid,  and 
ammonia  is  one  of  the  impurities  given  off  with  the  hydro- 
carbon gases.     These  are  all  passed  through  a  tank  filled 
with  water,   which  absorbs  the  ammonia  and   forms  an 
aqueous  solution,  known  as  aqua  ammonia  or  ammonium 
hydroxide.    This,  more  or  less  impure,  is  drawn  off  at  inter- 
vals and  treated  with  hydrochloric  acid,  which  converts  it 
into  a  salt  of   ammonia,  ammonium  chloride,  NH4C1,  as 
shown  by  the  following  reaction  :  — 

NH4OH  +  HC1  =  NH4C1  +  H2O. 

11.  Then  by  treating  this  chloride   with  some  strong 
alkali  like  caustic  potash  or  soda,  and  heating,  ammonia 
is  again  liberated,  and  being  passed  into  water,  produces 


NITROGEN  AND  ITS  COMPOUNDS 


75 


the  aqua  ammonia  of   commerce.      The  following  shows 
the  reaction  which  takes  place  :  — 

NH4C1  +  KOH  =  NH3  +  KC1  +  H2O. 

12.  On  account  of  its  cheapness,  slaked  lime,  Ca(OH)2, 
a  compound  very  similar  in  properties  to  caustic  potash  or 
soda,  is  ordinarily  used  with  the  sal  ammoniac  to  liberate 
the  ammonia.  The  reaction  is  seen  below  :  — 


2  NH4C1  +  Ca(OH)2  =  2  NH3  +  CaCl 


2  H2O. 


FIG.  18.  —  Preparation  of  Ammonia. 

m,  «,  o,  cylinders  containing  solutions  of  impure  ammonium  chlo- 
ride, as  obtained  from  coal-gas  factories,  mixed  with  lime ;  S,  S,  S, 
stirrers  to  keep  the  lime  from  settling ;  F,  furnace  to  heat  the  mixture 
and  expel  the  ammonia:  P.  B,  condensers  for  cooling  the  ammonia 
gas ;  C,  cylinder  of  pure  water  to  absorb  the  ammonia  and  thus  form 
aqua  ammonia ;  7),  trough  of  acid  to  combine  with  any  fumes  escap- 
ing from  C-  In  this  trough,  if  hydrochloric  acid  is  used,  there  would 
form  ammonium  chloride. 

EXPERIMENT  42.  —  To  illustrate  the  preparation  of  ammonia.  Put 
about  a  half  gram  of  sal  ammoniac,  NH4C1,  into  a  test-tube  and  add 
to  it  about  1  cc.  of  water,  then  a  little  caustic  soda  or  potash  solution, 


7G  MODERN  CHEMISTRY 

and  heat  gently.  Is  there  any  gas  given  off  having  an  odor?  Hold 
in  the  mouth  of  the  test-tube  a  piece  of  moistened  red  litmus  paper 
and  note  the  effects.  Try  also  a  piece  of  turmeric  paper  in  the  same 
way.  How  is  it  affected  ? 

EXPERIMENT  43.  —  To  about  2  g.  of  ammonium  chloride  in  a 
tube  or  flask  add  1  or  2  cc.  of  slaked  lime,  made  by  adding  a  little 
water  to  some  lime ;  adjust  upon  a  ring-stand  and  attach  a  delivery 
tube.  Warm  the  flask  gently  and  collect  a  jar  of  the  gas  by  upward 
displacement,  as  described  in  appendix.  To  tell  when  the  flask  is 
filled,  hold  near  the  mouth  a  piece  of  red  litmus  paper,  as  in  the  pre- 
ceding experiment.  Keeping  the  bottle  inverted,  insert  a  burning 
taper  up  into  the  bottle.  Does  ammonia  burn?  Does  it  support 
combustion  ? 

13.  Peculiarities  of  Ammonia.  —  Ammonia  is  a  colorless 
gas  having  a  strong  pungent  odor,  and  if  inhaled  in  con- 
siderable quantities  produces  strangulation  and  fills  the 
eyes  with  tears.     It  is  lighter  than  air,  having  a  density  of 
0.59  ;  it  will  not  support  combustion,  nor  burn  in  the  air; 
but  in  oxygen  a  jet  if  ignited  will  continue  to  burn  for 
some  time  with  a  yellow  flame.     It  has  remarkable  affinity 
for  chlorine,  as  will  be  seen  when  we  come  to  study  that 
gas.     It   also  combines  readily  with    hydrochloric    acid, 
forming  dense  white  fumes.     This  will  be  noticed  if  two 
bottles,  one  of  each,  be  opened  close  together.     It  is  well 
shown  also  in  the  following  experiment. 

EXPERIMENT  44. —  Put  into  a  bottle  two  or  three  drops  of  strong 
hydrochloric  acid  and  cover  with  a  glass  or  paper.  Now  fill  another 
bottle  with  ammonia  gas  and  invert  over  the  bottle  containing  the  acid. 
Remove  the  cover  separating  the  two  and  notice  the  results. 

14.  Solubility  in  Water.  —  Ammonia  is  very  soluble  in 
water,  as  the  following  experiments  will  show. 

EXPERIMENT  45.  —  Fill  the  bottle  again  with  ammonia  gas  as 
before  and  place  it  mouth  downward  into  a  basin  of  water.  Let  it 
stand  two  or  three  minutes  and  notice  whether  the  water  rises  in  the 
bottle. 


NITROGEN  AND  ITS  COMPOUNDS 


15.  Ammonia  Fountain.  —  The  most  striking  illustration 
of  the  solubility  of  ammonia  in  water  is  the  "ammonia 
fountain." 

EXPERIMENT  46.  —  Fit  to  a  round-bottomed  flask  or  strong  bottle, 
of  a  gallon  capacity  or  more,  a  rubber  cork  through  which  passes  a 
long  glass  tube  that  will  reach  half  way  to  the 
bottom  of  this  flask  and  nearly  to  the  bottom 
of  another  similar  one.  Draw  out  the  upper 
end  to  a  jet.  Fasten  in  position  or  hold  over 
the  lower  bottle  or  jar  as  shown  in  the  figure. 
To  the  water  in  the  lower  flask  add  a  few 
drops  of  some  acid  and  a  little  litmus  solution, 
or  a  few  drops  of  phenol-phthalein  solution. 
Now  fill  the  upper  flask  with  ammonia  as 
in  Experiment  44,  or  by  warming  gently  a 
solution  of  strong  aqua  ammonia  —  the  latter 
will  be  much  quicker  —  and  collecting  by  up- 
ward displacement  as  before.  When  well 
filled,  quickly  insert  the  cork  and  long  jet- 
tube  and  support  upon  the  other  flask  of 
water,  as  shown  in  Fig.  19.  In  a  few  sec- 
onds the  water  will  begin  to  rise  in  the 
tube,  owing  to  the  gradual  absorption  of 
the  ammonia,  and  will  soon  flow  into  the 

upper  flask.  The  absorption  then  will  be  very  rapid,  and  the  water 
will  be  forced  up,  forming  a  beautiful  fountain.  As  it  enters  the 
upper  flask  it  will  change  in  color,  owing  to  the  effect  of  the  ammonia 
upon  the  litmus  or  the  phenol  put  into  the  solution. 

16.  Effect  of  Heat  on  the  Solubility  of  Ammonia.  —  At 

0°  C.  one  liter  of  water  will  absorb  about  1150  liters  of 
ammonia.  As  the  temperature  rises,  the  amount  absorbed 
rapidly  decreases.  This  is  seen  in  the  fact  that  if  a  few 
cubic  centimeters  of  aqua  ammonia  in  a  flask  be  warmed 
gently,  the  gas  bubbles  out  so  rapidly  that  the  liquid 
seems  to  be  boiling  vigorously  when  it  scarcely  feels 
more  than  warm  to  the  hand. 


FIG.  19.  —  Ammonia 
Fountain. 


78  MODERN  CHEMISTRY 

17.  Effects  of  Platinum  and  Charcoal  on  Ammonia.  — 

If  a  small  flask  containing  strong  ammonium  hydroxide  be 
warmed  gently,  and  a  spiral  of  platinum  wire  previously 
heated  to  redness  be  held  in  the  neck  of  the  flask,  the  wire 
will  continue  to  glow  for  a  considerable  time.  Ammonia 
is  also  absorbed  rapidly  by  charcoal. 

EXPERIMENT  47.  —  To  show  absorption 
of  ammonia  by  charcoal. 

Fill  a  large  test-tube  with  ammonia  and 
place  it  inverted  over  an  evaporating  dish 
containing  a  quantity  of  mercury,  as  shown 
in  the  figure.  Slip  under  the  tube  a  piece 
of  charcoal.  In  two  or  three  minutes  the 
mercury  will  begin  to  rise  in  the  tube  to 
fill  the  space  formerly  occupied  by  the 
FIG.  20.  gaSt 

18.  Uses  of  Ammonia.  —  Immense  quantities  of  ammonia 
are  manufactured  and  used  annually.     For  cleansing  pur- 
poses and  for  softening  or  "  breaking  "  water  it  is  found 
in  almost  every  household.     In  a  medicinal  way  it  is  used 
as  a  restorative  in  cases  of  fainting,  and  overdoses  of  chlo- 
roform and  other  anaesthetics.      Considerably  diluted  it 
is  employed  in  neutralizing  the  effects  of  acids  upon  the 
clothing  or  upon  the  hands  and  face ;  in  a  similar  way, 
by  inhaling  it  cautiously,  it  will  counteract  the  effects  of 
chlorine,  bromine,  sulphur  dioxide,  and  similar  irritating 
gases. 

19.  As  a  Refrigerant.  —  Perhaps  the  most  extensive  use 
of  ammonia  is  as  a  refrigerant  in  the  manufacture  of  ice. 
The  principle  underlying  this  process  is  as  follows  :    Am- 
monia may  be  readily  liquefied  by  moderate  pressure  ;  if 
this  pressure  is  suddenly  removed,  very  rapid  evaporation 
takes  place,  producing  a  low  degree  of  cold. 


NITROGEN  AND  ITS  COMPOUNDS 


79 


EXPERIMENT  48.  —  To  show  the  freezing  of  water  by  rapid  evapora- 
tion. Put  upon  a  block  of  wood  a  few  drops  of 
water,  and  upon  this  a  watch  crystal.  Into  the 
crystal  pour  1  or  2  cc.  of  carbon  disulphide,  and 
blow  a  current  of  air  by  means  of  a  blowpipe 
across  the  liquid.  By  the  time  the  disulphide  is 
all  evaporated  the  crystal  will  be  frozen  tightly 
to  the  block.  Lift  the  block  by  taking  hold  of  the  crystal. 


FIG.  21. 


<  20.  Manufacture  of  Ice.  —  It  is  upon  the  same  principle 
that  ice  is  manufactured.  The  first  apparatus  for  this 
purpose  was  devised  by  Carre,  and  is  shown  in  the 


i  ii 

FIG.  22.  —  Carre's  Apparatus. 

accompanying  figure.  (I)  a  is  a  tank  containing  strong 
ammonia  water,  underneath  which  a  fire  is  placed.  This 
causes  the  ammonia  to  bubble  out  of  the  water  very 
rapidly,  whereupon  it  flows  over  into  6,  and  there  liquefies 
by  its  own  pressure,  the  water  surrounding  it  keeping  it 
cool,  c  is  a  cylinder  of  pure  water  fitting  into  6. 

21.  After  a  half  hour  or  so,  when  the  ammonia  has 
about  all  been  driven  out  of  the  solution  in  a,  the  posi- 
tion of  the  two,  a  and  6,  is  reversed  (II).  A  partial 


80 


MODERN  CHEMISTRY 


vacuum  forms  in  a  as  it  cools,  the  ammonia  in  b  begins 

to  evaporate  to  fill  the  vacuum, 
and  as  fast  as  it  flows  over 
into  a  is  absorbed  by  the  water 
there.  The  rapid  evaporation 
is  thus  kept  up  for  a  consider- 
able time,  and  the  cylinder  c, 
containing  pure  water  sur- 
rounded by  the  ammonia 
chamber  6,  has  its  contents 
frozen. 

22.  Manufacture  of  Ice  for  Commerce. — The  first  ice 
machines  used  for  the  manfacture  of  ice  upon  a  large  scale 
were  made  upon  this  principle.  At  present,  however,  in- 
stead of  creating  a  vacuum  by  cooling  A,  pumps  are  used 
to  remove  the  vapor  from  B  as  fast  as  it  forms.  This 
causes,  as  in  the  other  class  of  ice  machines,  a  rapid  evap- 
oration and  a  consequent  cooling  of  the  adjacent  water. 


FIG.  23.  —Cross-sectional  View  of 
Carre's  Apparatus. 


NHB 


FIG.  24.  — Modern  Ice  Plant. 

23.  Figure  24  will  show  the  essentials  of  the  improved 
methods  of  ice  manufacture.  A  is  a  strong  cylindrical 
tank  containing  liquid  ammonia.  0  is  a  large  rectangular 
vat  filled  with  strong  salt  water,  through  which  are  coiled 
a  series  of  pipes,  xx,  which  connect  with  A.  Through  the 


NITROGEN  AND  ITS  COMPOUNDS  81 

top  of  this  vat  are  let  down  oblong  galvanized  iron  boxes 
containing  the  water  to  be  frozen.  They  are  thus  sur- 
rounded by  the  salt  water  through  which  the  ammonia 
pipes,  32?,  pass.  P  is  a  pump  worked  by  steam,  which  is 
continually  exhausting  the  pipes  and  keeping  up  a  rapid 
evaporation  in  A.  The  pump,  at  the  same  time  that  it 
exhausts  xx,  is  also  condensing  the  ammonia  again  in  the 
tank  M,  from  which,  at  intervals,  it  is  allowed  to  flow 
back  again  by  the  pipe  y  into  A.  In  this  way  the  ammo- 
nia is  used  over  and  over  without  appreciable  loss.  The 
rapid  evaporation  lowers  the  temperature  of  the  salt 
water  in  0  below  the  freezing  point  of  pure  water,  and 
in  from  36  to  60  hours  the  ice  is  ready  to  be  drawn  from 
the  boxes. 

24.    Oxides  of  Nitrogen.  —  There  are  five  of  these  com- 
pounds, though  not  all  are  of  much  importance.     They 


Nitrous  Oxide,  Laughing  Gas,  or  Nitrogen  Monoxide,  N2O 

Nitric  Oxide,  Nitrogen  Dioxide NO 

Nitrous  Anhydride,  Nitrogen  Trioxide  ....  N2O3 
Nitrogen  Peroxide,  Nitrogen  Tetroxide  ....  NO2 
Nitric  Anhydride,  Nitrogen  Pentoxide  ....  N2O5 

The  formulae  for  the  second  and  fourth,  for  certain 
reasons,  are  sometimes  written  N2O2  and  N2O4. 

25.  Nitrous  Oxide. — This  is  ordinarily  called  "  laugh- 
ing gas."  It  has  been  stated  already  that  many  of  the 
compounds  of  nitrogen  are  unstable.  So,  if  we  heat  am- 
monium nitrate,  NH4NO3,  it  first  melts,  then  begins  to 
boil,  and  is  decomposed  to  form  nitrous  oxide  and  water, 
thus :  — 

NH4N03  +  heat  =  N2O  +  2  H2O. 


82  MODERN  CHEMISTRY 

EXPERIMENT  49.  — Put  into  a  test-tube  1  or  2  g.  of  ammonium 
nitrate,  attach  a  delivery  tube,  and  suspend  upon  an  iron  ring-stand. 
Heat  moderately  and  collect  two  or  three  small  bottles  of  the  gas  over 
warm  water.  Be  careful  not  to  heat  so  strongly  as  to  cause  a  vigorous 
ebullition,  lest  some  of  the  impurities  always  present  in  the  nitrate 
may  be  carried  over  and  thus  vitiate  the  nitrous  oxide.  When 
two  or  three  bottles  of  the  gas  have  been  collected,  remove  the 
cork  and  notice  the  odor.  Has  the  gas  any  color?  Test  a  bottle 
of  it  with  a  glowing  pine  splinter  as  you  did  the  oxygen.  What 
are  the  results  V  Try  also  a  small  piece  of  phosphorus  ignited ;  how 
does  it  burn  V 

26.  Peculiarities  of  Nitrous  Oxide.  —  Laughing  gas  is 
colorless,  somewhat  heavier  than  air,  having  the  odor  of 
sugar  when  being  heated  or  slightly  burned.     It  is  solu- 
ble to  a  considerable  extent  in  cold  water,  will  not  burn, 
but  supports  the  combustion  of  most  bodies  nearly  as  well 
as  oxygen.     Upon  the  human  system  it  acts  as  an  intoxi- 
cant, producing  first  a  sense  of  hilarity,  and  afterward 
unconsciousness.      Because  of  this  fact  it  is  frequently 
used  in  a  purified  form  as  an  anaesthetic  in  dentistry.     It 
is  easily  liquefied  by  cold  and  pressure,  and  is  generally 
used  in  this  form. 

27.  Nitric  Oxide,  NO.  —  This  gas  is  almost  always  one 
of  the  products  formed  when  a  metal  is  treated  with  nitric 
acid. 

EXPERIMENT  50.  —  Into  a  flask  put  2  or  3  g.  of  copper  turnings, 
and  make  connections  as  for  collecting  oxygen  over  water.  Add  a 
few  cubic  centimeters  of  nitric  acid,  somewhat  diluted.  What  kind 
of  fumes  first  fill  the  flask?  Notice  that  they  disappear,  being  carried 
over  and  dissolved  in  the  water.  Collect  three  or  four  bottles  of  the 
gas.  What  can  you  say  of  its  color  and  density?  Test  it  to  learn 
whether  it  will  burn.  Try  a  blazing  pine  splinter,  also  a  burning 
candle  in  the  gas ;  do  they  continue  to  burn  ?  Try  also  in  a  deflagrat- 
ing spoon  a  well-ignited  piece  of  phosphorus ;  what  results  ?  Can  you 
explain  ? 


NITROGEN  AND  ITS  COMPOUNDS  83 

28.  Peculiarities  of  Nitric  Oxide.  —  As  seen  above,  it  is 
a  colorless  gas,  heavier  than  air,  is  non-combustible  and  a 
non-supporter   of   ordinary  combustion.      It   is   noticed, 
however,  that  substances  which  burn  with   great   heat, 
such  as  phosphorus,  sodium,  and  the  like,  continue  to 
burn  in  nitric  oxide  with  great  brilliancy.     The  reason 
is  apparent.     Ordinary  air  is  about  20  per  cent  oxygen  ; 
nitric  oxide  is  about  50  per  cent  oxygen  ;    such  bodies 
therefore   as  have  sufficient  heat  in  burning  to  decom- 
pose the  gas  continue   to   burn   more  brilliantly,  while 
those  which   kindle  at  a  low  temperature  have  not  the 
power  to  use  the  large  proportion  of  oxygen  present. 

29.  Affinity  for  Oxygen.  —  The  strongest  chemical  prop- 
erty of  the  gas  is  its  great  affinity  for  oxygen.     This  is 
seen  whenever  it  is  allowed  to  escape  into  the  air,  brown 
fumes  of  nitrogen  tetroxide  being  formed. 

EXPERIMENT  51.  —  Into  a  bottle  of  nitric  oxide  inverted  over  a 
basin  of  water,  pass  slowly  a  current  of  oxygen.  This  may  be  gener- 
ated in  a  test-tube  by  using  a  small  amount  of  potassium  chlorate  and 
manganese  dioxide,  or  by  treating  the  latter  with  sulphuric  acid. 
Notice  how  the  colorless  gas  changes;  what  else  happens? 

30.  Two  molecules  of  nitric  oxide  unite  with  one  of 
oxygen,  O2,  as  follows  :  — 

2  NO  +  O2  =  2  N02. 

If  two  or  three  drops  of  carbon  disulphide  be  put  into  a 
bottle  of  nitric  oxide  and  allowed  to  stand  a  few  minutes, 
or  until  the  disulphide  vapor  has  filled  the  bottle,  on  the 
approach  of  a  flame  the  mixture  of  gases  will  burn  with  a 
brilliant  flash,  pale  violet  in  color. 

31.  Nitrous   Anhydride,  N203. — The   term,  anhydride, 
means  without  water,  and   is   applied  to   certain  oxides, 
which,  when  water  is  added  to  them,  form  acids;   that 


84  MODERN  CHEMISTRY 

is,  the  anhydride  is  the  acid  without  the  water.  Such 
oxides  were  formerly  called  acids,  and  carbon  dioxide  is 
sometimes  even  now  spoken  of  as  carbonic  acid  ;  but  all 
true  acids  contain  hydrogen,  and  theoretically  at  least 
are  formed  by  adding  water  to  the  oxide  or  anhydride. 
Nitrogen  trioxide  is  thus  the  anhydride  of  nitrous  acid,  and 
is  of  interest  to  us  only  because  of  this  fact.  Thus  :  — 

N203  +  H20  =  2  HN02. 

In  this  case  if  the  oxide  is  passed  into  water  it  is  readily 
absorbed,  forming  nitrous  acid,  as  shown  by  the  reaction. 

EXPERIMENT  52.  —  Into  an  evaporating  dish  put  a  little  starch, 
and  with  a  little  water  rub  it  to  a  thick  paste.  Transfer  this  to  a 
test-tube  into  which  you  have  put  about  2  cc.  of  nitric  acid.  Attach 
a  delivery  tube  and  let  the  end  dip  into  15  or  20  cc.  of  water  in  a 
bottle  or  flask.  Heat  the  starch  in  the  test-tube  for  some  time,  or 
until  the  fumes  are  given  off  readily.  What  color  are  they?  When 
the  gas  ceases  to  come  over,  test  the  solution  in  the  bottle  with  blue 
litmus  paper  to  learn  whether  it  is  acid  in  character.  You  should 
thus  obtain  nitrous  acid  from  the  brown  fumes  of  nitrogen  trioxide 
which  were  driven  off. 

Let  us  test  it  to  determine.  Put  one  or  two  cubic  centimeters  of 
the  solution  into  a  test-tube  and  add  a  few  drops  of  a  solution  of 
ferrous  sulphate,  made  by  dissolving  a  crystal  of  the  salt  in  water. 
Does  it  turn  brown  in  color  ?  If  so,  nitrous  acid  is  indicated. 

32.  Instability  of  Nitrous  Acid.  —  Although  it  is  char- 
acteristic of  nitrogen  compounds  to  decompose  readily, 
nitrous  acid  is  more  unstable  than  most  of  the  others.  In 
fact,  it  breaks  up  of  its  own  accord  at  ordinary  temperatures. 

EXPERIMENT  53. — Put  a  part  of  the  nitrous  acid  prepared  above 
into  a  test-tube,  and  when  it  has  been  standing  a  few  minutes,  or 
when  gently  warmed,  hold  a  sheet  of  white  paper  behind  the  tube  and 
notice  carefully  whether  brown  fumes  are  being  given  off.  Continue 
to  heat  gently  for  a  few  minutes,  or  until  these  do  not  seem  to  appear, 
and  test  with  blue  litmus  paper.  Is  the  solution  still  acid  ?  If  so,  test 


NITROGEN  AND  ITS  COMPOUNDS 


85 


FIG.  25. 


a  part  of  it  to  determine  whether  it  is  still  nitrous  acid.  If  it  is,  warm 
it  a  little  longer  and  test  again.  If  not,  test  it  for  nitric  acid.  This 
is  usually  done  thus :  To  about  1  cc.  of  the  solution  to  be  tested  add 
about  as  much  strong  sulphuric  acid;  shake  the  two  together  and  cool 
well  by  holding  the  tube  in  a  stream  of  cold  water. 

Next  prepare  a  fresh  solution  of  ferrous  sulphate,  and  pour  it  very 
cautiously  upon  the  solution  to  be  tested  so  as  not  to  mix  them.  To 
do  this  it  will  be  necessary  to  hold 
the  two  tubes  almost  in  a  horizontal 
position,  as  shown  in  the  figure,  and 
let  the  ferrous  solution  run  slowly 
upon  the  other.  Set  aside  the  tube 
in  a  vertical  position  and  let  it 
stand  for  a  few  minutes,  when  a 
dark  brown  ring  should  have 
formed  at  the  junction  of  the  two 
liquids.  The  test  requires  consid- 
erable care,  but  is  very  satisfactory 
when  well  done.  The  test  is  not  distinctive,  however,  if  nitrous  acid 
is  present,  as  this  also  will  form  a  ring ;  but  the  latter  ring  is  usually 
much  broader  and  forms  much  more  quickly.  A  simpler  plan  is  to 
drop  a  crystal  of  ferrous  sulphate  into  the  solution  to  be  tested,  and 
then  pour  down  the  side  of  the  tube  upon  it  a  little  sulphuric  acid. 
A  brown  ring  forms  about  the  ferrous  sulphate. 

33.  Nitrogen   Tetroxide,   N02. — This  gas   is   of  little 
importance,  yet  it  is  one  frequently  seen  in  the  action  of 
nitric  acid  upon  metals  in  the  presence  of  air.     We  noticed 
that  when  nitric  oxide  was  exposed  to  the  air  it  quickly 
turned  brown.     So  when  a  metal  is  treated  with  ordinary 
nitric  acid,  the  nitrogen  dioxide  at  first  formed  quickly 
unites  with  oxygen  from  the  air  and  forms  the  brown 
fumes  of  nitrogen  tetroxide.     For  experimental  purposes 
it  may  be  prepared  directly  by  heating  almost  any  nitrate. 

34.  Characteristics  of  Nitrogen  Tetroxide.  —  It  is  at  ordi- 
nary temperatures  a  brownish  red  gas,  heavier  than  air, 
having  a  very  offensive  suffocating  odor;    is   non-com- 


86  MODERN  CHEMISTRY 

bustible  and  a  non-supporter  of  ordinary  combustion.  It 
is  soluble  in  water,  as  may  be  seen  by  inverting  a  bottle 
of  it  over  water.  The  brown  fumes  will  disappear  and 
the  water  will  rise  in  the  bottle. 

35.  Nitrogen  Pentoxide,  N205.  — The  only  fact  of  inter- 
est in  connection  with  this  compound  is  its  relation  to 
nitric  acid,  of   which  it  is  the  anhydride.      Hence  it  is 
often  called  nitric  anhydride.     The  relation  is  exhibited 
in  the  following  reaction  :  — 

N205  +  H20  =  2  HN03. 
Hi 

36.  Nitric  Acid,  HN03.  —  When  a  strong  electrical  dis- 

'  charge  takes  place  in  the  air,  as  in  the  case  of  violent 
thunder  storms,  small  quantities  of  the  nitrogen  and  oxy- 
gen are  caused  to  unite,  forming  nitrogen  oxides,  which 
dissolved  in  the  falling  rain  form  nitric  acid.  This  is 
sometimes  in  appreciable  quantities.  Compounds  of  nitric 
acid,  such  as  sodium  and  potassium  nitrate,  are  found  in 
abundance,  especially  the  former.  These  salts  are  now 
known  to  be  produced  by  the  action  of  certain  bacteria 
upon  nitrogenous  matter,  and  in  some  countries  the  sodium 
nitrate  needed  is  prepared  by  introducing  these  bacteria. 

37.  Formation  of  Nitric  Acid.  —  Nitric  acid  may  be  ob- 
tained by  decomposing  any  nitrate  with  sulphuric  acid. 

EXPERIMENT  54.  —  Put  into  a  retort  40  or  50  g.  of  sodium  nitrate, 
NaNO3,  cover  with  concentrated  sulphuric  acid,  and  insert  the  long 
neck  of  the  retort  into  a  flask  surrounded  with  ice  and  salt,  as  in 
Fig.  26.  Instead,  the  retort  may  be  connected  with  a  short  Liebig 
condenser,  kept  cool  by  a  stream  of  water.  Apply  a  moderate  heat 
to  the  retort ;  nitric  acid  will  distil  over  and  condense  in  the  receiver. 
The  reaction  may  be  represented  in  two  ways,  according  to  the  amount 
of  Chile  saltpeter  used  :  — 

2  NaNO3  +  H2SO4  =  Na2SO4  +  2  HNO3. 
NaNO3  +  H2SO4  =  NaHSO4  +  HNO3. 


NITROGEN  AND  ITS  COMPOUNDS  87 


FIG.  26.  —  Preparation  of  Nitric  Acid. 

38.  It  will  be  remembered  that  we  prepared  ammonia, 
a  volatile  compound,  by  treating  a  salt  of  ammonia  with 
caustic  lime,  a  compound  of  similar  properties  which  is 
not  volatile.     In  exactly  the  same  way  nitric  acid  may  be 
easily  expelled  from  a  liquid  by  heating,  while  sulphuric 
acid  cannot  be.     The  latter,  therefore,  simply  takes  the 
place  of  the  former  in  combination  with  the  metal,  and 
the  nitric  acid  boils  out  and  condenses  in  the  receiver. 
This  is  shown  in  the  above  reactions. 

39.  Characteristics  of  Nitric  Acid.  — Aqua  fortis,  as  this 
acid  is  frequently  called,  is  colorless  when  pure,  though, 
owing  to  impurities  present,,  it  is  generally  slightly  yellow- 
ish in  color.      It  is  a  volatile  acid  and  gives  off  fumes 
which  are  very  irritating.     It  colors  the  skin  and  finger 
nails   yellow,    and    the    color   is   intensified   rather   than 
removed   by  the   application   of   ammonia.       Like   other 
strong  acids,  it  attacks  all  organic  matter,  rapidly  destroys 
the  fibres  of  clothing,  and  the  discoloration  of  the  cloth 
cannot  be  removed  by  the  application  of  any  alkali,  as 
is  the   case  with   other  acids.      Though  a  comparatively 
stable  compound,  a  flask  of  it  exposed  to  bright  sunlight,  or 


88  MODERN  CHEMISTRY 

heated,  soon  becomes  filled  with  a  brownish  gas,  nitrogen 
peroxide,  NO2,  and  oxygen.  This  is  seen  in  the  follow- 
ing reaction :  — 

2  HN03  +  heat  =  O  +  H2O  +  N2O4. 

On  account  of  this  property  of  giving  up  a  part  of  its 
oxygen  with  moderate  ease  it  is  frequently  used  as  an 
oxidizing  agent.  This  is  seen  in  the  following  experi- 
ments :  — 

EXPERIMENT  55.  —  Warm  slightly  a  little  turpentine  in  an  evap- 
orating dish  and  pour  upon  it  some  strong  or  fuming  nitric  acid. 
Usually  only  a  copious  evolution  of  fumes  is  the  result,  but  sometimes 
the  oxidation  is  so  rapid  that  the  whole  mass  bursts  into  a  flame. 

EXPERIMENT  56.  —  Heat  in  an  iron  spoon  a  few  small  pieces  of 
charcoal ;  when  red  hot  drop  quickly  into  a  beaker  containing  some 
strong  nitric  acid.  Notice  that  the  charcoal  continues  to  glow  for 
some  little  time,  owing  to  the  oxygen  obtained  from  the  acid ;  notice 
also  that  brown  fumes  fill  the  beaker.  Upon  a  small  quantity  of 
warm  strong  nitric  acid  in  an  evaporating  dish,  drop  a  very  small 
piece  of  phosphorus.  Notice  that  it  is  instantly  set  on  fire,  and  small 
particles  are  thrown  out  in  all  directions. 

EXPERIMENT  57.  —  To  a  little  tin-foil  in  a  test-tube  add  some  strong 
nitric  acid  and  heat.  Notice  that  the  metal  is  not  dissolved,  but  con- 
verted into  a  white  solid,  which  is  really  an  oxide  of  tin  in  combina- 
tion with  water,  SnO2,  H2O.  By  heating,  the  water  is  evaporated 
and  the  oxide  remains. 

40.  Uses   of   Nitric   Acid. — Nitric  acid   finds   a   great 
many  uses  in  the  laboratory,  frequently  as  an  oxidizing 
agent,  as  will  be  seen  from  time  to  time.     It  is  used  con- 
siderably in  the  manufacture  of  sulphuric  acid,  which  will 
be  described  later,  and  in  making  nitro-glycerine  and  other 
explosives. 

41.  Aqua  Regia.  —  This  is  a  mixture  of  nitric  and  hydro- 
chloric acids  in  the  proportion  of   one  of  the  former  to 
three  of  the  latter,  and  is  so  named  because  it  will  dis- 


NITROGEN  AND  ITS  COMPOUNDS  89 

solve  gold,  the  "king  of  the  metals."  It  is  the  strongest 
solvent  known,  and  attacks  several  metals  which  are 
unaffected  by  single  acids. 

42.  Nitro-glycerine  and  Dynamite.  —  Nitro-glycerine  is 
prepared  by  treating  glycerine  with  a  mixture  of  fuming 
nitric  and  sulphuric  acids.     It  is  in  the  form  of  a  liquid, 
and  hence  not  convenient  for  uses  under  all  circumstances. 
Dynamite  differs  from  nitro-glycerine  in  that  it  contains 
about  25  per  cent  of  siliceous  or  infusorial  earth.     It  is, 
therefore,  more  convenient  and  less  liable  to  explode  by 
accident.     Guncotton  is  a  similar  compound  which  is  pre- 
pared by  treating  cotton  wool  with  nitric  and  sulphuric 
acids.    It  is,  therefore,  not  very  different  from  nitro-glycer- 
ine in  composition.    It  has  the  advantage  of  being  perfectly 
safe  when  wet,  and  is,  therefore,  kept  damp  when  carried 
on  board  men-of-war.     In  this  condition  it  is  exploded 
by  igniting  with  a  small  charge  of  fulminating  mercury. 
Its  combustion  is  five  hundred  times  as  rapid  as  that  of 
the  best  gunpowder.     The  heavy  charges  now  used  for  tor- 
pedoes give  an  impact  that  no  man-of-war  can  withstand. 
All  of  these  explosives,  as  well  as  gunpowder,  are  valuable 
because  of  the  great  instability  of  the  nitrates  present  or 
formed  in  the  preparation  of  them. 

ARGON  :   A  =  40  ? 

43.  Its  Discovery.  —  For  some  time  previous  to  the  dis- 
covery of  argon,  in  1894,  it  had  been  observed  that  nitro- 
gen obtained  from  the  atmosphere  was  heavier  than  that 
from  its  compounds.      In  that  year  Lord  Rayleigh  and 
Professor  Ramsay  observed  that,  by  passing  atmospheric 
nitrogen  over  red-hot  magnesium,  a  small    residue  was 
obtained  which  could  not  be  made  to  enter  into  combina- 
tion.    This  residue  was  the  new  gas  now  called  Argon. 


90  MODERN  CHEMISTRY 

Its  name  comes  from  the  Greek  word  argon,  which  means 
idle  or  inactive. 

44.  Characteristics  of  Argon.  —  This  element  is  an  odor- 
less, colorless  gas,  somewhat  heavier  than  air,  constituting 
about  eight-tenths  of  one  per  cent  of  the  atmosphere.  As 
far  as  is  known  it  is  a  perfectly  inert  substance,  hitherto 
resisting  all  attempts  to  make  it  enter  into  combination. 
No  compounds  of  the  gas  being  known,  it  is  impos- 
sible to  assign  it  a  positive  atomic  weight,  but  it  is 
believed  to  be  about  forty. 

SUMMARY  OF  CHAPTER 

Origin  of  the  term  nitrogen. 

Abundance  of  the  element  and  of  certain  compounds. 

Easiest  method  of  preparing  nitrogen. 

What  is  the  purpose  of  the  phosphorus  ? 
The  source  of  the  nitrogen  ? 

Would  a  candle  do  as  well  as  phosphorus  ?    Why  ? 
Two  other  ways  of  preparing  nitrogen. 

Chemical  action  in  each  case. 
Characteristics  of  nitrogen. 

Compare  with  oxygen  and  hydrogen  —  How  similar  —  How 

different. 
How  test  each  ? 
Compounds  of  nitrogen. 

Ammonia  —  How  formed  in  nature. 

Old  method  of  preparing  "  hartshorn." 
Present  source  of  ammonia. 
Wherein  are  these  three  methods  similar  ? 
Characteristics  of  ammonia. 

Experiments  to  illustrate  these. 
Uses. 

Experiments  to  illustrate  the  most  impor- 
tant. 

Carre's  ice  machine. 
Present  ice  machines. 


THE  ATMOSPHERE  91 

Oxides  of  nitrogen. 

Names  and  formulae. 

Most  important.     Why? 

Method  of  preparing  this  one. 

Use  —  Physiological  effects. 
Acids  of  nitrogen. 

Names  and  formulae. 

Anhydride  of  each  —  Meaning  of. 

How  distinguish  each  by  test. 

Preparation  of  nitric  acid. 

Characteristics  and  uses  of. 

Aqua  regia. 

Explosives  —  Explanation  of  their  explosive  character. 


CHAPTER   VIII 
THE  ATMOSPHERE 

1.  What  it  is. — We  are  living  at  the  bottom  of  an 
ocean  as  wonderful  as  the  watery  one  that  washes  the 
shores   of   our   continent.       The   atmosphere   covers   the 
entire  earth  to  a  depth  variously  estimated  at  from  fifty 
to  two  hundred  miles.     Some  of  the  recent  investigators 
believe  that,  in  an  extremely  attenuated   form,  the  air 
extends  through  space,  even  reaching  and  commingling 
with  the  atmospheres  of  other  planets.      Centuries  ago 
the  air  was  regarded  as  one  of  the  elements,  just  as  water 
was,  and  the  other  gases,  as  discovered,  were  all  called 
air  ;  for  example,  hydrogen  was  known  as  inflammable  air, 
carbon  dioxide  as  fixed  air,  etc.     So  the  perfumes  that 
were  exhaled  from  various  flowers  were  regarded  as  air, 
slightly  changed  in  some  unknown  way. 

2.  Constituents  of  the  Air. — We  know  now  that  the 
air  is  not  an  element,  but  a  mixture  of  several  substances. 
Three   of   these,  nitrogen,  oxygen,  and   argon,  are  con- 


92  MODERN  CHEMISTRY 

stant,  but  the  watery  vapor  and  carbon  dioxide  vary  from 
time  to  time.  Many  efforts  have  been  made  to  learn 
whether  the  air  is  a  compound  of  oxygen  and  nitrogen, 
mixed  with  the  other  constituents  named.  Analyses  have 
been  made  in  all  parts  of  the  world,  thousands  of  feet 
above  the  earth,  in  the  crowded  cities,  on  the  North  and 
South  American  prairies  ;  but  though  the  proportion  of 
the  gases,  79  of  nitrogen  to  21  of  oxygen,  by  volume,  is 
found  in  all  cases  approximately  the  same,  yet  the  varia- 
tion is  too  great  to  permit  one  to  believe  that  they  are 
united  to  form  a  compound.  The  argon  constitutes  about 
1  per  cent  of  what  has  usually  been  taken  as  nitrogen,  or 
about  0.8  per  cent  of  the  air.  The  carbon  dioxide  varies 
somewhat,  but  seldom  amounts  to  more  than  three  or  four 
parts  in  10,000,  except  in  poorly  ventilated  rooms.  The 
aqueous  vapor  varies  greatly.  When  the  air  contains  all 
it  is  able  to  hold,  it  is  said  to  be  saturated,  or  to  contain 
100  per  cent.  Ordinarily,  however,  the  humidity  is  not 
above  60  to  70  per  cent.  The  amount  may  be  estimated 
by  passing  a  certain  volume  of  air  through  a  tube  filled 
with  calcium  chloride  and  noting  the  increase  of  weight. 

3.  Diffusion  of  Gases.  —  We  find  that  the  air  contains 
five  gases,  of  densities  ranging  all  the  way  from  nine  to 
forty  times  that  of  hydrogen.  Were  it  not  for  the  law 
of  diffusion,  we  should  find  the  argon,  perhaps,  nearest 
the  ground.  The  next  above  this,  forming  a  layer  twelve 
feet  or  more  deep,  would  be  the  carbon  dioxide;  then 
the  oxygen,  nitrogen,  and  water  vapor,  in  the  order 
named.  Such  conditions  would  be  fatal  to  all  animal 
life.  As  it  is,  however,  owing  to  the  constant  circula- 
tion of  the  atmosphere  and  the  rapid  diffusion  of  gases, 
no  more  carbon  dioxide  is  found  close  to  the  surface  of 
the  earth  than  hundreds  of  feet  above.  Two  or  three 


THE  ATMOSPHEEE  93 

exceptions  to  this  ought  to  be  noted,  among  them  the 
deadly  Upas  Valley,  where  the  carbon  dioxide  is  exhaled 
from  volcanic  sources  more  rapidly  than  diffusion  can 
carry  it  away.* 

4.  Boyle's   Law. — Many  years   ago  Boyle  discovered 
and   formulated  the    law,    which    now   bears    his   name, 
that  the  volume  of  a  gas,  the  temperature 

remaining  constant,  varies  inversely  as  the 
pressure.  In  other  words,  if  we  double 
the  pressure,  the  volume  decreases  by 
half  ;  or  if  we  lessen  the  pressure  by  half, 
the  volume  becomes  twice  as  great.  In  the 
accompanying  figure  we  have  10  cc.  of  the 
gas,  a,  under  the  pressure  of  the  atmos- 
phere,  simply  confined  by  the  mercury  in 
the  bottom  of  the  bent  tube  ;  if  now  we  pour  in  more 
mercury  at  the  open  end,  the  volume  of  a  will  constantly 
decrease,  and  when  we  have  added  as  much  as  corre- 
sponds to  the  pressure  of  an  additional  atmosphere,  the 
volume  will  have  decreased  to  5  cc. 

5.  Standard  Pressure.  — Atmospheric  pressure  is  meas- 
ured by  the  barometer,  which  at  sea  level  stands  about 
30  in.  high.     In  chemical  calculations,  however,  we  use 
the  metric  system,  and  the  equivalent  of  30  in.  is  760  mm. 
Hence  when  we  say  that  a  gas  is  under  standard  pressure, 
we  mean  760  mm. 


*  This  valley  is  located  in  the  island  of  Java,  is  about  a  half  mile  in 
circumference  and  thirty-five  feet  deep,  surrounded  at  no  great  distance 
by  hills.  The  bottom  is  comparatively  smooth  and  is  devoid  of  vegeta- 
tion. Loudon,  in  describing  his  visit  there,  says  that  "  skeletons  of  human 
beings,  tigers,  pigs,  deer,  peacocks,  and  all  sorts  of  birds"  are  to  be  seen 
everywhere,  bleached  by  the  exposure  till  they  are  as  white  as  ivory.  A 
fowl  thrown  in  died  in  one  and  a  half  minutes. 


94  MODERN  CHEMISTRY 

PROBLEM.  —  500  cc.  of  oxygen  under  standard  pressure  would  be 
how  much  under  750  mm.?  As  the  pressure  has  decreased,  the 
volume  would  have  increased.  We  would  solve  then  by  the  fol- 
lowing proportion  :  — 

F:  F'::P':P; 

or  500  cc.  :  a:::  750:  760. 


If  desired,  this  problem  may  be  solved  without  using  a  proportion. 
As  the  pressure  has  decreased,  we  know  that  the  volume  will  be  corre- 
spondingly increased  ;  that  is, 

V  will  equal  |f£  of  F; 
or  V  =  m  x  500. 

V1  =  ? 

2.  What  volume  would  300  cc.  of  hydrogen,  at  750  mm.  pressure, 
occupy  at  780  mm.  pressure  ? 

3.  25  liters  of  air  at  380  mm.  pressure,  would  be  how  many  at  5 
atmospheres'  pressure  V 

6.  Law  of  Charles.  —  Just  as  heat  causes  solids  and 
liquids  to  expand,  so  it  affects  gases.  In  the  case  of 
the  latter  the  rate  of  expansion  is  practically  constant,  and 
is  in  the  Law  of  Charles  stated  thus  :  The  pressure  re- 
maining constant,  all  gases  expand  or  contract  uniformly 
under  the  same  increase  or  decrease  of  temperature.  This 
has  been  studied  carefully,  and  it  has  been  proven  that 
for  an  increase  or  decrease  of  1°  C.,  a  volume  of  gas  ex- 
pands or  contracts  2T_  of  the  volume  it  occupies  at  0°  C. 
To  illustrate,  suppose  we  have  in  a  vessel  273  cc.  of 
oxygen  at  0°  C.  If  by  any  means  the  temperature  is 
raised  to  10°  C.,  the  volume  would  increase  -^fa  of  273  cc. 
or  10  cc.,  and  would  occupy  283  cc.  It  obviously  follows 
from  this  that  were  the  law  to  hold  true,  and  were  the  gas 
reduced  to  a  temperature  of  273°  below  zero,  it  would 
disappear  entirely.  However,  all  gases  thus  far  tried 


THE  ATMOSPHERE 


95 


become  liquids  before  reaching  this  low  temperature,  so 
that  the  law  no  longer  applies. 

7.  Absolute  Zero.  —  From  the  fact  that  a  gas  would 
disappear  entirely  at  273°  below  zero,  according  to  the 
Law  of  Charles,  —  273°  has  been  called  absolute  zero,  the 
point  at  which  the  molecules  of  a  body  would  have  no 
vis  viva,  or  absolutely  no  heat  energy.      This  point  has 
never  yet  been  reached,  though  recent  investigators  have 
approached  within  a  few  degrees  of  it.     It  is  necessary  to 
have  a  clear  understanding  of  what  is  meant  by  the  abso- 
lute zero,   as  it  is  used  in  making  all  calculations   for 
correction  of  the  volume  of  gases  for  temperature. 

8.  The  Absolute  Thermometer. — In   Fig.  28  we  have 
the  Fahrenheit,   Centigrade,  and  Absolute  thermometers 
represented    in    F,    0,    and    A, 

respectively.  It  must  be  re- 
membered that  the  last  is  not  a 
thermometer  really  in  existence, 
but  serves  merely  for  illustra- 
tion.  The  boiling  points  on  the 
three  are  marked  212°,  100°,  and 
373°;  the  freezing  points  32°, 
0°,  and  273°.  The  absolute  zero 
therefore  would  }>e  the  same  as 
—  273°  on  the  Centigrade,  as 
the  degrees  on  these  two  are  of 
the  same  size.  Let  us  apply 
this  in  a  problem. 


o 


10$ 


273- 


A 
373°- 


273 


o- 


-Freezing  Pt. 


FIG.  28. 


PROBLEM.  —  500  cc.  of  oxygen  at  0°  C.  would  occupy  what  volume 
at25°C.? 

Expressing  Charles's  Law  in  the  form  of  a  proportion,  we  would 
have 

F:F::*:f, 


96  MODERN  CHEMISTRY 

in  which  V  and  t  represent  the  volume  and  temperature  of  the  gas  at 
the  beginning  of  the  experiment,  and  V  and  t'  at  the  end  ;  and  it 
must  be  remembered  that  t  and  t'  always  mean  absolute  temperatures. 
Applying  this  to  the  problem,  we  see  that  t  =  0°  C.,  or  273°  A.,  and 
t'  =  273  +  25,  or  298°  A.  Substituting,  we  have  :  — 

500  :  V  :  :  273  :  298. 
v,  _  298  x  500 
273 

PROBLEM  2.  —  What  volume  would  250  cc.  of  gas  at  20°  C.  occupy 
at  -10°C.? 

Here,  t  =  20°  C.  =  273  +  20  =  293°  A. 

t  =  -  10°  C.  =  273  -  10  =  263°  A. 
F=250cc. 

Substituting,  250  :  V  :  :  293  :  263. 

T/,  =  250  x  263 
293 

PROBLEM  3.  —  If  400  cc.  of  hydrogen  is  heated  from  —  15°  C.  to 
30°  C.,  what  volume  would  the  gas  then  occupy? 

PROBLEM  4.  —  What  would  be  the  result  in  problem  2,  if  at  the 
same  time  the  barometer  fell  from  760  mm.  to  740  ? 

This  may  be  solved  by  first  finding  the  value  of  F',  as  shown  above 
at  the  temperature  t',  and  substituting  this  in  the  proportion  for 
determining  V  under  P'  pressure.  Suppose,  in  problem  2  above, 
F'  =  225+,  then  solving  for  pressure,  we  would  have 

V"  =  |fS  of  225  +  ; 

or  F:  F"::P":P'; 

or  225  :  V"  :  :  740  :  760. 

T//,  =  225  x  760 
740 

Or  the  problem  may  be  solved  by  using  a  compound  proportion  :  — 


250  :  x  :  :  j  ^  +^  :  273       L°  ;  293  x  740  x  =  263  x  760  x  250. 

PROBLEM  5.  —  500  cc.  of  gas  under  4  atmospheres  and  at  -  25°  C. 
would  have  what  volume  at  760  mrn.  and  at  20°  C.  ? 

Let  the  teacher  furnish  a  number  of  similar  problems  for  practice. 


THE  ATMOSPHERE  97 

9.    Weight  of  Air.  —  The  weight  of  a  liter  of  air  may 
easily  be  found  by  the  following  experiment :  — 

EXPERIMENT  58.  —  M  in  the  figure  is  a  flask 
of  about  500  cc.  capacity.  Fit  to  it  a  cork  with 
a  glass  tube  somewhat  drawn  out,  as  shown. 
Put  into  the  flask  about  50  cc.  of  water  and 
boil  for  several  minutes,  so  as  to  expel  all  the 
air.  Immediately  remove  the  cork  and  insert 
another,  not  perforated.  When  the  flask  has 
cooled  to  the  temperature  of  the  room,  weigh 
the  whole.  Suppose  this  to  be  m.  Remove  the 
cork,  thus  allowing  the  air  to  enter,  and  again 
weigh  flask  and  cork.  Suppose  this  to  be  n. 
The  gain  in  weight,  FIG.  29. 

n  —  m  =  wt.  of  air  in  flask. 

To  determine  the  volume  of  the  air  contained,  take  a  graduated  flask, 
or  cylinder,  and  fill  the  flask  M  with  water.     Suppose  this  to  be  r  cc. 

Then 

r  cc.  of  air  weighs  n  —  m  grams, 

from  which  the  weight  of  1000  cc.  =  1  liter  may  be  determined. 

10.  Liquefaction  of  Air.  —  The  air  is  so  well  known  that 
it  is  not  necessary  to  say  anything  regarding  its  proper- 
ties.    At  the  present  time,  however,  considerable  atten- 
tion is  being  given  to  it  in  the  liquid  form.      A  large 
number  of  experiments  with  it  have  been  made  by  Dewar, 
Pictet,  Linde,  Tripler,  and  others,  with  a  view  to  ascer- 
taining its  properties  and  practical  value.     It  is  said  that 
the  first  ounce  of   liquid  air  ever  produced  cost  about 
13000   and   the    next    pint   about    $80;    with    improved 
methods,  however,  it  may  now  be  prepared  for  a  few  cents 
per  gallon. 

11.  Dewar's  Bulbs. — Dewar  has   invented   a   double- 
walled  glass  globe  in  which  liquid  air  may  be  kept  for 
a  number  of  hours  with  little  loss;   here  in  this  country 


98  MODERN  CHEMISTRY 

it  is  often  shipped  several  hundred  miles  in  large  double- 
walled  tin  cans,  heavily  lined  with  felt,  but  at  the 
expense  of  20  to  40  per  cent  of  the  liquid.  The  Dewar 
bulbs  vary  somewhat  in  construction,  but  the  general 

plan  is  the  same  in  all.  Into 
the  space  between  the  inner 
and  outer  walls  of  the  globe, 
a  drop  or  two  of  mercury  is 
introduced;  the  air-pump  is 
then  attached,  and  a  vacuum 
of  very  high  degree  obtained. 

F,a.  30-Dewar's  Buibs.  As  the  air  is  PUmPed   OUt'  the 

mercury  vaporizes  and  fills  the 

space.  When  liquid  air  is  introduced  into  the  inner  globe, 
the  mercurial  vapor  is  condensed  upon  the  outer  surface 
of  the  inside  flask,  and  forms  a  perfect  mirror.  Thus  we 
have  not  only  a  vacuous  chamber,  but  also  a  mirror  to 
prevent  the  access  of  heat  rays  to  the  liquid  air,  and  the 
insulation  is  well  nigh  perfect.  A  modified  form  of 
this  Dewar  bulb,  holding  about  two  gallons,  is  now  used 
for  shipping  liquid  air.  The  insulation  is  so  perfect 
that  the  liquid  may  be  kept  two  weeks  with  little  loss. 
It  is  obvious  that  the  ordinary  closed  tank  is  unsuit- 
able on  account  of  the  high  pressure  which  would  soon 
obtain. 

12.  Linde's  Apparatus.  — The  plan  used  for  liquefying 
air  may  be  understood  from  the  accompanying  figure, 
which  represents  the  apparatus  used  by  Linde.  P  is  a 
pump  which,  when  the  piston  is  raised,  opens  a  valve  at 
G-  and  allows  the  air  from  D  to  enter;  as  the  piston 
descends,  the  valve  Gr  closes  and  H  opens.  The  air  is 
thus  forced  up  through  the  coils  in  the  tank  J",  kept  cold 
by  running  water,  and  passes  on  through  B.  At  C  the 


THE  ATMOSPHERE 


99 


pipe  B  enters  within  a  larger  one,  and  continues  thus 
until  at  the  point  E  it  again  emerges.  The  ingoing  cur- 
rent of  air  flows"  through  the  inner  pipe  under  pressure 
and  issues  from  a  small  aperture  at  R  into  a  chamber,  T, 
under  low  pressure.  As  expansion  is  a  cooling  process, 
the  air  is  thus  reduced  in  temperature  ;  at  the  next  stroke 


Used  by  Courtesy  of  the  Scientijic  American. 

FIG.  31.  —  Linde's  Apparatus  for  liquefying  Air. 

of  the  piston  the  vacuum  formed  in  the  pump  again  opens 
the  throttle  valve  at  6r,  and  the  cooled  air  in  T  flows  back 
through  the  outer  pipe,  back  through  D.  As  this  opera- 
tion is  constantly  repeated,  the  outgoing  current  being 
cooled  by  its  expansion  into  T,  continually  lowers  the 
temperature  of  the  ingoing  current,  until  finally  liquid 
air  will  trickle  down  into  the  chamber  T,  and  may  be 
drawn  off  at  Fmuch  the  same  as  water  from  a  reservoir. 


100  MODERN  CHEMISTRY 

13.  Effects  of  Liquid  Air  upon  Certain  Substances.  —  It 

is  found  that  such  articles  as  rubber,  beefsteak,  eggs,  etc., 
immersed  in  liquid  air,  become  exceedingly  brittle ;  while 
an  ordinary  tin  cup  dipped  into  the  liquid  and  dropped 
upon  the  floor  breaks  into  fragments  like  glass.  All  these 
effects  are  due  to  the  intense  degree  of  cold  of  the  liquid 
air,  and  not  to  any  chemical  action. 

14.  As  the  boiling  point  of  nitrogen  is  lower  than  that 
of   oxygen,  the  former  boils   out   the  more  rapidly,  and 
in  a  short  time  a  vessel  of  liquid  air,  freely  exposed,  will 
contain  almost  pure  liquid  oxygen.      If  into  this  a  red- 
hot  iron  rod  be  thrust,  it  will  burn  vigorously,  notwith- 
standing the  fact  that  the  temperature  of  the  surrounding 
liquid  is  nearly  1700°  C.  below  the  melting  point  of  iron. 
It  should  be  said,  however,  that  the  two  are   probably 
not  in  contact,  but  that  a  layer  of  gaseous  oxygen  next  to 
the  iron  rod  supports  the  combustion.      Felt,  saturated 
with  liquid  air,  burns  explosively,  and  if  confined  in  metal 
tubes,  bursts  them  with  violence. 

15.  Practical  Uses  of  Liquid  Air. — Numerous  applica- 
tions for  liquid  air  have  been  suggested,  but  as  yet  these 
are  in  the  experimental   stage.      Among  them   may  be 
named  the  following  :    (1)  as  a  substitute  for  compressed 
air ;   (2)  as  a  refrigerant ;   (3)  in  blasting  ;   (4)  in  surgery 
for  removing   diseased   tissues   without   the    use    of   the 
knife  ;   (5)  as  a  smoke  consumer,  and  for  burning  garbage 

in  cities. 

SUMMARY  OF  CHAPTER 

Composition  of  the  atmosphere. 

Old  ideas  of  the  air. 

Present  ideas. 

Explanation  of  uniformity  of  composition. 
Boyle's  Law  —  Statement  of. 

Meaning  of  term  standard  pressure. 


THE  HALOGENS  101 


Charles' Law  —  statement  o£.   - 

Meaning  of  term  absolute  ^^\  *' 

Problems. 
Density  of  air.  \  ,  //'  i     j  *"  '-  -" 

Methods  of  finding  weight  of  one  liter. 
Liquefaction  of  air. 

Present  method. 

Dewar  bulbs. 

Effects  of  liquid  air. 

Suggested  uses. 


CHAPTER   IX 
THE  HALOGENS 

1.  Members  of  the  Group.  —  The  term  halogen  is  from 
two  Greek  words,  meaning  salt  producer,  and  is  given  to 
this  group  of  elements  because  with  the  metals  they  form 
a  large  number  of   salts.      The  group  includes  fluorine, 
chlorine,  bromine,  and  iodine.     The  first  two  are  gases,  the 
third  a  liquid,  and  the  fourth  a  solid.    They  possess  prop- 
erties  very   similar   to   each    other,    differing   in   degree 
rather  than  otherwise.     It  will  be  found  that  as  the  atomic 
weights  increase,  the  chemical  activity  decreases. 

FLUORINE  :  F  =  19 

2.  Characteristics.  —  Fluorine  is  an  element  which  had 
not  been  prepared  until  a  few  years  ago.     It  is  a  greenish- 
colored  gas,  of  a  very  irritating  odor,  and  readily  attacks 
almost  all  substances.     By  extreme  cold  and  pressure  it 
has  been  liquefied,  and  when  in  that  condition  loses  much 
of  its  chemical  activity.    It  is  of  little  practical  value,  and 
is  considered  only  because  of  one  or  two  compounds  which 
it  forms. 


102  MODERN  CHEMISTRY 

3.  .  Compomid£  of  Fluorine. — There  is  only  one  com- 
pound cf  this  elem-8'ai  m  which  we  are  specially  interested, 
a.ud.  ;that  is  hy4roflu9ric  »acid,  HF.      It  is  prepared  by 
treating   iludr   spar,    calcium   fluoride,    with   strong   sul- 
phuric acid,  the  reaction  being  — 

CaF2  +  H2S04  =  CaS04  +  2  HF. 

Hydrofluoric  acid  is  a  very  irritating,  colorless  gas,  which 
readily  dissolves  or  corrodes  glass,  and  hence  is  sometimes 
used  in  glass  etching. 

EXPERIMENT  59.  —  Warm  a  sheet  of  glass  3  or  4  in.  square  by 
holding  it  at  some  height  above  the  burner  flame,  and  drop  upon  it 
a  few  shavings  of  paraffine.  Move  the  glass  about  so  as  to  distribute 
the  melted  wax  evenly,  and  allow  it  to  cool.  Now  with  a  sharp  pen- 
cil or  stylus  draw  any  desired  figure  in  the  wax,  being  sure  to  cut 
through  to  expose  the  glass.  Lay  this  face  down  over  a  lead  saucer,* 
into  which  you  have  put  about  2  g.  of  calcium  fluoride  and  as  much 
strong  sulphuric  acid.  Support  upon  a  ring-stand  and  warm  for  a 
minute  very  gently,  so  as  not  to  melt  the  wax.  In  a  few  minutes  the 
etching  should  be  completed.  This  can  be  determined  by  testing 
with  the  point  of  a  knife  blade,  when  the  glass  will  feel  rough  where 
the  figure  was  drawn  in  the  wax.  When  the  experiment  is  finished, 
the  paraffine  may  be  removed  with  a  dull  knife  or  by  immersing  in 
warm  water. 

CHLORINE:  01  =  35.5 

4.  History.  —  Chlorine,  the  most  important  element  of 
the  halogen  group,  was  first  prepared  by  Scheele  in  1774, 
in  treating  black  oxide  of   manganese  —  the  same  com- 
pound we  have  used  in  preparing  oxygen  —  with  hydro- 
chloric acid.     He  did  not  know,  however,  that  he  had 
discovered  a  new  element,  but  supposed  it  to  be  a  com- 

*  Instead  of  the  lead  saucer  a  small  evaporating  dish  may  be  used.  If 
so,  notice  whether  it  also  is  attacked  on  the  inside  by  the  hydrofluoric 
acid. 


THE  HALOGENS  103 

pound  of  oxygen  and  hydrochloric  acid,  and  called  it 
dephlogisticated  marine  acid  air.  Hydrochloric  acid  was 
then  called  marine  acid.  Later,  when  chlorine  was  found 
to  be  an  element,  it  was  given  its  present  name  from 
the  Greek  word  chloros,  meaning  green. 

5.  How  found.  —  Because  of  its  great  chemical  affinity, 
chlorine,  like  fluorine,  is  never  found  uncombined.      Its 
most  widely  distributed  compound  is  common  salt,  NaCl, 
which  is  found  in  extensive  deposits  in  nearly  all  parts  of 
the  United  States,  and  constitutes  a  large  per  cent  of  the 
solids  held  in  solution  in  the  ocean. 

6.  How  to  prepare  Chlorine.  —  For  laboratory  purposes 
the  simplest  way  of  preparing  chlorine  is  that  used  by  its 
discoverer,  by  treating  manganese  dioxide  with   hydro- 
chloric acid  and  warming  gently. 

EXPERIMENT  60.  —  Into  a  good-sized  test-tube  or  generating  flask 
put  1  or  2  g.  of  manganese  dioxide  and  about  2  cc.  of  hydrochloric 
acid.  Attach  a  delivery  tube  and  warm  gently.  Collect  two  or  three 
bottles  of  chlorine  by  downward  displacement,  as  described  on  page 
362,  and  preserve  for  future  experiments  in  studying  its  properties. 

7.  The  reaction  that  takes  place  in  preparing  chlorine 
as  above  may  be  indicated  thus  :  — 

Mn02  +  4  HC1  =  C12  +  MnCla  4-  2  H2O. 

From  this  we  see  that  only  half  the  chlorine,  in  the  hydro- 
chloric acid  used,  is  obtained  free,  the  other  half  having 
united  with  the  manganese  to  form  manganese  chloride,  a 
compound  which  has  no  application  in  the  arts.  An 
immense  quantity  of  chlorine  is  used  every  year  in  the 
manufacture  of  bleaching  powder,  and  cost  of  production 
is  a  very  important  consideration.  The  method  described 
above  is,  therefore,  not  strictly  followed  commercially, 
but  is  so  modified  that  the  manganese  chloride  is  converted 


104  MODERN  CHEMISTRY 

into  the  dioxide  again.  This  is  much  cheaper,  and  is 
known  as  the  Weldon  process. 

8.  The  Weldon  Process.  —  In  the  preparation  of  chlorine 
$  ]  for  manufacturing  processes,  pyrolusite,  a  natural  ore  of 
manganese  and  an  impure  form  of  the  dioxide,  is  treated 
with  hydrochloric  acid  in  large  stone  tanks.  When  the 
chlorine  is  no  longer  given  off,  any  excess  of  acid  in  the 
residual  liquor  is  neutralized  with  common  limestone, 
finely  powdered.  The  reaction  may  be  represented  thus  : — 

MnCl2  +  H20  +  2  HC1  +  CaCO3 

=  MnCl2  +  CaCl2  +  CO2  +  2  H2O. 

/Residual  liquor  and  excess\  ,  nimestone)  =  /mixture  manganese  and  cal-\ 
\  of  acid  /  \  cium  chloride  in  water.  / 

Therefore,  we  now  have  a  mixture  of  manganese  chloride 
and  calcium  chloride  in  solution.  Next,  lime  water,  pre- 
pared by  treating  ordinary  lime  with  water,  is  added. 

CaO  (lime)+  H2O  =  Ca(OH)2  (lime  water). 

This  precipitates  the  manganese  in  the  form  of  the  hydrox- 
ide, Mn(OH)2,  thus :  - 

1  +  Ca(OH)2  =  Mn(OH)2  +  2  CaCl2. 
^vg  J 

Now  by  heating  this  and  at  the  same  time  passing  a  cur- 
rent of  air  through  the  solution,  the  manganese  hydroxide, 
Mn(OH)2,  is  converted  into  the  dioxide,  thus :  — 

Mn(OH)2  +  O  (air)=  MnO2  +  H2O. 

The  calcium  chloride,  being  very  soluble,  remains  in  solu- 
tion. The  mixture  is  now  allowed  to  flow  into  settling 
basins,  where  the  dioxide  is  slowly  deposited  as  a  dark- 


THE  HALOGENS  105 

colored  ooze,  known  as  Weldoris  mud.  This  is  now  ready 
to  be  passed  again  into  the  stills  for  a  second  treatment 
with  hydrochloric  acid.* 

9.  The  Chemical  Changes  in  the  Above  Method. — By 
studying  the  reaction 

MnO2  +  4  HC1  =  MnCl2  +  2  H2O  +  C12, 

we  see  that  the  oxygen  in  the  manganese  dioxide  has  been 
set  free  from  the  manganese  and  has  united  with  the  hy- 
drogen in  the  acid ;  or,  as  we  sometimes  say,  the  chlorine 
has  been  set  free  by  the  oxidation  of  the  hydrogen  with 
which  it  was  combined.  In  like  manner  other  substances, 
besides  manganese  dioxide,  may  be  used  with  hydrochloric 
acid  in  preparing  chlorine.  In  every  instance  the  princi- 
ple is  the  same  :  the  oxygen  is  first  set  free,  and,  combining 
with  the  hydrogen  in  the  acid,  liberates  the  chlorine.  Let 
us  prove  this. 

EXPERIMENT  61.  —  Treat  a  few  crystals  of  potassium  chlorate, 
KC1O3,  a  substance  from  which  we  obtained  oxygen,  with  a  little 
hydrochloric  acid.  Warm  very  gently  if  necessary  to  start  the  action, 
and  then  remove  the  test-tube  from  the  flame.  Notice  the  rapid  evo- 
lution of  gas.  With  the  chlorine  thus  obtained  we  have  also  an  oxide 
of  chlorine,  C1O2,  as  seen  in  the  reaction 

4  KC1O3  +  12  HC1  =  4  KC1  +  9  Cl  +  3  C1O2  +  6  H2O. 

Add  to  this  a  few  cubic  centimeters  of  water,  which  will  give  a 
yellowish  solution  known  as  euchlorine  or  chlorine  water.  Preserve  it 
in  a  dark-colored,  tightly  stoppered  bottle. 

*  It  perhaps  ought  to  be  stated  that  a  small  excess  of  lime  water  usu- 
ally remains  mixed  with  the  precipitated  manganese  hydroxide.  When 
the  current  of  air  is  passed  through  the  solution,  this  lime  water,  Ca(OH)2, 
forms  with  a  portion  of  the  manganese  hydroxide,  calcium  manganite, 
CaMnO3,  which  may  be  regarded  as  CaO .  MnO2.  This,  with  hydrochloric 
acid,  yields  chlorine,  as  does  manganese  dioxide. 


106  MODERN  CHEMISTRY 

10.  It  will  be  remembered  that  we  prepared  oxygen 
also  by  using  potassium  dichromate.     If  now  we  treat  this 
compound  with  hydrochloric  acid,  chlorine  is  obtained  as 
in  the  other  instances. 

11.  Practical  Application  of  this  Principle. — In  all  the 
above  methods  the  chlorine  is  set  free  by  bringing  into 
contact  with  hydrochloric  acid  some  highly  oxygenized 
substance  which  will  give  up  a  part  of  its  oxygen  to  unite 
with  the  hydrogen  of  the  acid.     Hence  was  conceived  the 
idea  of  using  atmospheric  oxygen  as  the  most  economical 
source  of  supply. 

12.  Deacon's  Process.  —  This  idea  is  applied  in  Deacon's 
process.      Theoretically  the  reaction  that  takes  place  ac- 
cording to  this  method  is  as  follows  :  — 

2  HC1  +  O  =  H20  +  C12. 

In  reality,  however,  the  process  is  not  so  simple.  In  the 
preparation  of  oxygen  from  potassium  chlorate  and  man- 
ganese dioxide,  we  have  seen  that  the  latter  compound 
remains  unchanged.  It  acts,  as  was  said,  by  catalysis,  in 
a  manner  not  thoroughly  understood,  causing  the  potas- 
sium chlorate  to  yield  up  its  oxygen  at  a  temperature 
much  lower  than  would  otherwise  affect  it. 

13.  The  Catalytic  Agent.  —  In  Deacon's  process  for  the 
preparation  of  chlorine  some  catalytic  agent  is  necessary, 
because  a  mixture  of  oxygen  and  gaseous  hydrochloric 
acid,  when  heated,  is  only  slightly  decomposed.      As  a 
catalytic   agent  some  such   compound  of   copper  as  the 
sulphate  or  the  chloride  is  used.      Clay  balls  or  bits  of 
brick  are  saturated  with  the  copper  solution  and  placed  in 
an  iron  pipe  called  the  decomposer.     Through  this  the 
mixed  gases,  air  and  hydrochloric  acid,  previously  heated 
to  about  500°  C.,  are  made  to  pass.     The  acid  is  oxidized 


THE  HALOGENS  107 

and  the  chlorine  set  free.  The  chemical  action  of  the 
cuprous  chloride,  Cu2Cl2,  is  not  thoroughly  understood  ; 
but  it  is  believed  that  two  or  three  reactions  take  place, 
in  the  course  of  which  cupric  chloride,  CuCl2,  is  formed, 
which  at  the  temperature  present  is  unstable  and  gives  up 
a  part  of  its  chlorine,  leaving  cuprous  chloride  again. 

14.  Another  Method  of  preparing  Chlorine.  —  Another 
method  is  frequently  employed  in  the  laboratory  instead 
of  the  first  one  given. 

EXPERIMENT  62.  —  Into  a  test-tube  put  a  small  quantity  of  common 
salt,  NaCl,  mixed  with  a  little  manganese  dioxide,  and  about  a  cubic 
centimeter  of  sulphuric  acid.  Warm  gently.  Is  there  any  evidence 
that  chlorine  is  being  generated  ? 

15.  Comparison  of  the  Two  Methods.  —  We  shall  find 
that  when  common  salt  is  heated  with  sulphuric  acid  they 
react  with  each  other,  forming  hydrochloric  acid.     That  is 
what  we  have  done  in  this  case.     We  see  by  comparing 
the  two  reactions, 


and 


Mn02  +  4  HC1  =  MnCl2  +  2  H2O  +  C12 


2HaSO4=MnSO4+NaaSO4+2HaO+Cla, 

that  in  the  first  case  we  treated  the  dioxide  directly  with 
hydrochloric  acid,  but  in  the  second  indirectly  by  the  use 
of  two  substances,  which  in  reacting  prepare  the  hydro- 
chloric acid  needed.  It  will  be  seen,  however,  in  the  sec- 
ond instance  that  all  the  chlorine  is  set  free,  while  in  the 
first  only  one-half. 

16.  It  is  probable  that  in  the  second  case  the  reaction 
is  a  little  more  complicated,  perhaps  as  follows  :  — 

First,  a  part  of  the  sulphuric  acid  reacts  with  the  com- 
mon salt,  forming  hydrochloric  acid,  thus  :  — 

2  NaCl  +  H2S04  =  2  HC1  +  Na2SO4. 


108  MODERN  CHEMISTRY 

Then  another  part  reacts  with  the  manganese  dioxide 
also  present,  setting  free  oxygen,  as  we  have  seen  before, 
thus  :  — 

MnO2  +  H2SO4  =  MnSO4  +  H2O  +  O. 

Then  this  nascent  oxygen  immediately  attacks  the  hydro- 
chloric acid  present,  oxidizing  it  and  liberating  the  chlorine, 
thus  :  — 

2  HC1  +  O  =  H2O  +  C12. 

Putting  these  three  reactions  together,  we  would  have 


17.  Experiments  with  Chlorine.  —  With  the  chlorine 
prepared  make  the  following  experiments  in  study  of  its 
properties  :  — 

EXPERIMENT  63.  —  Note  the  color  of  the  gas;  the  odor.  Put  a 
burning  match  into  a  bottle  of  chlorine  ;  try  also  a  burning  candle. 
State  the  results.  Does  the  gas  burn?  Does  it  support  combustion? 

EXPERIMENT  64.  —  To  show  its  chemism  for  certain  metals.  Sift 
into  a  bottle  of  chlorine,  by  means  of  a  fine  wire-gauze  spoon,  some 
powdered  metallic  antimony;  try  in  the  same  way  metallic  arsenic. 
Describe  the  results. 

EXPERIMENT  65.  —  To  show  the  chemism  of  chlorine  for  hydrogen. 
In  a  room  partially  darkened,  fill  a  strong  bottle  with  chlorine  and 
hydrogen,  mixed.  Wrap  a  towel  about  it,  ignite  a  piece  of  magnesium 
ribbon,  and  bring  it  toward  the  mouth  of  the  bottle.  A  violent  explo- 
sion is  the  result.  Bright  sunlight  has  the  same  effect.  Try  also  the 
following  experiment  to  show  the  same  fact. 

EXPERIMENT  66.  —  Attach  a  jet  to  a  hydrogen  generator,  H,  and 
when  it  has  been  in  action  long  enough  to  expel  all  the  air,  ignite  it, 
and  insert  into  a  jar  of  chlorine,  C,  as  shown  in  Figure  32.  Does  it 
continue  to  burn?  How  does  the  flame  change  in  appearance  ?  What 
becomes  of  the  green  gas  ?  After  a  few  moments  add  about  1  or  2  cc. 
of  water  to  the  gas,  and  shake  well.  Drop  into  the  solution  a  piece  of 
blue  litmus  paper  ;  what  is  indicated  ?  It  is  best  to  dry  the  hydrogen 
by  passing  through  a  drying  tube,  D,  filled  with  calcium  chloride. 


THE  HALOGENS 


109 


FIG.  32. 


EXPERIMENT  67.  — To  show  affinity  of  chlorine  for  hydrogen  in 
compounds  of  the  latter.  Into  a  jar  of  chlorine  thrust  a  narrow  slip 
of  blotting  paper  which  has  been 
moistened  in  moderately  warm  tur- 
pentine. State  the  results.  Turpen- 
tine consists  of  carbon  and  hydrogen, 
C10H16.  What  has  the  chlorine  really 
done  ? 

EXPERIMENT  68.  —  Practical  appli- 
cation of  the  preceding  experiment. 
Into  a  jar  of  chlorine  pour  a  few  cubic 
centimeters  of  any  solution  containing 
organic  colors,  as  litmus,  logwood,  or 
carmine.  Shake  it  up  and  notice  the 
effects. 

EXPERIMENT  69.  —  With  the  same 
purpose  as  in  Experiment  68.  In 
another  jar  of  chlorine,  suspend  a 
piece  of  blue  or  pink  calico  mois- 
tened with  water.  Try  another  simi- 
lar piece  without  moistening  it.  Are  the  results  different? 

EXPERIMENT  70.  —  To  show  affinity  of  chlorine  for  ammonia.  At- 
tach to  a  small  flask,  into  which  you  have  put  25  or  30  cc.  of  strong 
aqua  ammonia,  a  delivery  tube  with  jet  attached.  Warm  the  flask 
gently  as  in  preparing  ammonia  for  the  "fountain,"  Experiment  46, 
and  insert  the  tube  into  a  bottle  well  filled  with  chlorine.  What 
happens?  What  becomes  of  the  chlorine? 

18.  Characteristics  of  Chlorine.  —  Chlorine  is  a  greenish 
yellow  gas,  with  a  very  irritating  odor,  producing  tem- 
porarily a  catarrhal  affection  of  the  nasal  passages.  It  is 
somewhat  soluble  in  water,  forming  a  solution  yellowish 
in  color,  with  the  characteristic  odor  of  chlorine.  This 
solution  is,  however,  unstable,  as  the  chlorine  gradually 
combines  with  the  hydrogen  of  the  water  to  form  hydro- 
chloric acid,  while  the  oxygen  is  set  free.  Chlorine  is 
about  two  and  a  half  times  as  heavy  as  air  and  does  not 
support  ordinary  combustion.  It  will  be  found,  however, 


110  MODERN  CHEMISTRY 

that  sodium  and  phosphorus,  when  well  ignited,  burn  vig- 
orously in  an  atmosphere  of  chlorine. 

EXPERIMENT  71.  —  Put  a  small  piece  of  sodium,  heated  in  a  defla- 
grating spoon  until  it  takes  fire,  into  a  bottle  of  chlorine.  State 
results.  Notice  the  white  deposit  of  common  salt  that  forms.  In 
the  same  way  try  a  piece  of  phosphorus,  without  first  igniting  it. 
State  results. 


19.  Chemical  Affinity  of  Chlorine.  —  From  our  experi- 
ments in  oxygen  we  learned  that  considerable  heat  was 
necessary  to  effect  its  rapid  union  with  any  other  element. 
The  iron  wire,  the  sulphur,  and  the  phosphorus,  all  had  to 
be  raised  to  the  kindling  point.     In  the  case  of  chlorine 
we  find  that  union  often  takes  place  at  ordinary  tem- 
peratures, showing  its  chemism  to  be  far  greater.     Thus 
arsenic  and  antimony  sprinkled  into  the   gas   took  fire 
spontaneously,  as  did  also  the  phosphorus  and  the  tur- 
pentine.    In  the  latter  case  the  chemical  action  is  due 
to  the  affinity  between  the  hydrogen  in  the  turpentine 
and  the  chlorine  ;   the  same  remarkable  affinity  of  these 
gases  for  each  other  was  also  seen  in  exploding  the  mix- 
ture of  the  two  by  means  of  light,  and  in  the  hydrogen 
jet  which  continued  to  burn  in  the  chlorine. 

20.  Chlorine  Hydrate.  —  If  a  saturated  solution  of  chlo- 
rine water  be  surrounded  by  a  mixture  of  ice  and  salt, 
in  a  few  minutes  yellowish  crystals  of  chlorine  hydrate, 
represented  by  the  formula  Cl,  5  H2O,  are  formed  through- 
out the  liquid.     Chlorine  may  be  liquefied  at  —  34°  C. 
under   ordinary   atmospheric   pressure,   or   at   0°  with  a 
pressure  of  six  atmospheres.     In  this  condition  it  is  of 
a  bright  yellow  color.      It  has   also  been   solidified   by 
reducing  to  102°  below  zero,  and   in  this  form  closely 
resembles  the  liquid  in  color. 


THE  HALOGENS 


111 


21.  Uses  of  Chlorine.  —  Chlorine  is  used  to  a  consider- 
able extent  in  the  extraction  of  gold  from  its  ores,  because 
it  is  a  good  solvent  of  that  metal.      A  large  amount  of 
that  now  used  for  this  purpose  is  put  up  at  the  factories 
in  the  liquid  form  in  steel  cylinders  lined  with  lead,  and 
then  shipped  wherever  desired. 

22.  As  a  Bleaching  Agent.  —  Chlorine   is   a  powerful 
bleaching  agent,  but  acts  indirectly.     We  noticed  that 
dry  calico  was  but  little  affected  by  chlorine.     The  reason 
for  this  is  that  chlorine  in  its  great  chemism  for  hydrogen 
abstracts  it  from  the  water,  and  the  nascent  oxygen  unites 
with  the  coloring  matter  of  the  cloth,  converting  it  into 
colorless  compounds  ;  whereas  in  the  dry  cloth  there  was" 
comparatively   little   moisture   to  furnish   the   necessary 
oxygen. 

23.  Its  most  extensive  use  in  manufactures  is  in  bleach- 
ing cotton  and  linen  goods  and  paper  pulp.     Here,  how- 
ever, it  is  used  in  the  form  of  bleaching  powder.     This  is 
a  compound,  which  when  treated  with  dilute  acid  readily 
gives  up  its  chlorine.     The  following  diagram  will  illus- 
trate the  method  employed  in  bleaching  cloth. 


FIG.  33.  —  Cloth-bleaching  Apparatus. 

The  cloth  is  seen  in  a  roll  at  A ;  from  here  it  passes 
down  under  rollers  at  the  bottom  of  the  vat  B,  which  con- 
tains bleaching  powder  in  water,  next  up  over  rollers  and 
down  into  a  second  vat  containing  dilute  hydrochloric  acid, 
into  a  third  vat  with  bleaching  powder,  and  so  on  until 
the  cloth  is  sufficiently  bleached.  The  excess  of  chlorine 


112  MODERN  CHEMISTRY 

must  now  be  removed,  or  it  will  attack  the  fibers  of  the 
cloth  and  make  them  weak.  To  prevent  this  the  cloth  is 
drawn  through  another  vat,  jD,  containing  an  antichlor ; 
that  is,  a  solution  which  combines  with  the  chlorine  still 
present  and  forms  such  compounds  as  will  not  attack  the 
fibres.  For  this,  sodium  thiosulphate  is  frequently  used. 
Then,  after  passing  through  a  vat  of  water  for  washing, 
the  cloth  comes  out  pure  and  white= 

Chlorine  is  also  used  to  some  extent  as  a  disinfectant, 
but  generally  in  the  form  of  bleaching  powder  for  this 
purpose  also. 

HYDROCHLORIC  ACID,  HC1 

24.  History.  —  This  acid,  sold  usually  under  the  name 
muriatic  acid,  has  been  known  for  four  centuries,  and  was 
formerly  called  spirit  of  salt.     Later  it  received  the  name 
of  marine  acid. 

25.  Where  found.  —  It  is  found   uncombined   only  in 
very  small  quantities.     It  is  said  to  exist  in  the  stomach 
and  to  aid  digestion,  and  is  sometimes  emitted  from  vol- 
canoes in  eruption. 

26.  How  to  prepare  Hydrochloric  Acid.  —  The  method 
of  preparation  has  already  been  suggested  in  one  of  the 
experiments  for  making  chlorine. 

EXPERIMENT  72. — Into  a  generating  flask  put  about  25  g.  of  sodium 
chloride,  NaCI,  and  cover  with  strong  hydrochloric  acid.  Then  add 
sulphuric  acid,  drop  by  drop,  by  means  of  a  separatory  funnel,  warm- 
ing gently.  Collect  two  or  three  bottles  of  the  gas  by  downward  dis- 
placement and  preserve  for  a  study  of  the  properties.  Keep  them 
covered  to  prevent  diffusion.  The  bottle  is  full  when  a  moistened 
piece  of  blue  litmus  paper  held  near  the  mouth  is  quickly  turned  red. 

27.  Manufacture  on  a  Large  Scale.  —  The  method  illus- 
trated by  this  experiment  is  really  the  one  used  in  prepar- 
ing hydrochloric  acid  on  a  large  scale.     It  is  nearly  all 


THE  HALOGENS 


113 


obtained  as  a  by-product  in  the  manufacture  of  soda  crys- 
tals preparatory  to  the  making  of  soap.  Like  many  other 
valuable  articles  of  commerce,  it  was  at  one  time  allowed 
to  go  to  waste  as  of  no  value. 

28.  In  the  manufacture  of  sodium  carbonate,  common 
salt  was  treated  with  sulphuric  acid  as  above,  and  the  gas 
obtained  was  allowed  to  escape  from  the  flues.     But  being 
heavier  than  the  air  it  settled  to  the  ground,  destroying 
vegetation  and  rendering  all   life   in   the   neighborhood 
almost  unendurable.     In  some  places  it  was  produced  so 
abundantly  as  to  corrode  even  the  tools  of  workmen.     It 
thus  became  so  great  an  evil  that  laws  were  passed  pro- 
hibiting any  manufacturer  from  allowing  the  escape  of 
such  gas,  just  as  the  consumption  of  coal  smoke  is  de- 
manded in  most  large  cities  to-day.     An  attempt  was  also 
made  to  conduct  the  gases  into  streams  of  water,  but  this 
resulted  in  the  death  of  animals  living  in  the  streams. 

29.  Finally  uses  were  found  for  the  acid,  and  then  plans 
were  thought  of  and  efforts  made  to  save  and  use  it.     The 
gas  is  conducted  into 

towers  filled  loosely 
with  coke,  down  which 
water  is  allowed  to 
trickle  slowly.  In  this 
way  the  gas  is  practi- 
cally all  absorbed,  and 
there  results  a  moder- 
ately strong  aqueous 
solution  of  hydrochlo- 
ric acid.  Sometimes 

FIG.  <*i.  —Hydrochloric  Acid  Factory. 

the  gases  are  conducted 

through  large  Woulff  bottles  partly  filled  with  water,  where 

solution  is  effected  in  the  same  way. 


114 


MODERN  CHEMISTRY 


The  reaction  that  takes  place  may  be  represented  as 

follows :  — 

NaCl  +  H2SO4  =  NaHSO4  +  HC1. 

If,  however,  the  heat  is  increased,  a  larger  amount  of 
hydrochloric  acid  is  obtained  by  using  the  same  amount 
of  sulphuric  acid  with  more  salt.  Thus  :  — 

2  NaCl  +  H2S04  =  Na2SO4  +  2  HCL 

30.  Experiments  with  Hydrochloric  Acid.  —  Many  char- 
acteristics of  hydrochloric  acid  may  be  learned  by  the 
following  experiments  :  — 

EXPERIMENT  73.  —  Into  a  bottle  of  the  gas  collected  above  put 
moistened  pieces  of  blue  and  red  litmus  paper.    How  are  they  affected  ? 
Lower  a  candle  into  the  bottle.     What  happens?    Does  the  gas  burn? 
EXPERIMENT  74.  —  To  show  the  solubility  of  the  gas  in  water. 
Add  to  a  bottle  of  hydrochloric  acid  gas  a  little  water  and  shake  for  a 
moment.   Hold  a  piece  of  moistened  blue  litmus  paper  within  the  bottle. 
Is  it  affected?    Drop  it  into  the  solution.    What  happens?    What  has 
the  water  done  ?    Has  the  solution  any  taste  ? 
EXPERIMENT  75.  —  Purpose  same  as  the 
preceding.       This  is   a   repetition    of    the 
"ammonia  fountain"  experiment.     In  pre- 
paring for  it  one  or  two  additional  points 
should  be  noticed.     It  is  better  to  use  appa- 
ratus somewhat  smaller  than  before,  and  the 
gas  must  be  collected  by  downward  displace- 
ment.    The  lower  flask  in  this  case  had  bet- 
ter be  fitted  with  a  two-hole  rubber  coik, 
through  one  of  which  the  long  tube  passes. 
Through  the  other  should  be  passed  a  short 
tube  bent  at  right  angles,  as  shown  in  the 
figure  accompanying. 

When  the  flask  is  well  filled  with  gas, 
make  the  connections  all  tight,  then  blow 
through  the  bent  tube  b  to  start  the  flow= 
Otherwise  it  will  be  necessary  to  wait  several 


Illlllllllllllllllllllllllllllllllllllllllllllllllllllllil 


FIG.  35.— Hydrochloric 
Acid  Fountain. 


THE  HALOGENS  115 

minutes  before  the  water  will  enter  the  upper  flask.  The  experiment 
works  well,  but  will  be  more  attractive  if  the  water  is  colored  by  lit- 
mus or  some  vegetable  solution  which  will  change  color  upon  absorbing 
the  acid  in  the  upper  flask.  A  drop  or  two  of  ammonia  and  a  few  of 
phenol  phthalein  in  the  water  serve  excellently.  The  deep  purplish 
red  solution  becomes  perfectly  colorless  as  it  enters  the  upper  flask. 

31 .  Characteristics  of  Hydrochloric  Acid.  —  Hydrochloric 
acid  is  a  colorless  gas,  somewhat  heavier  than  air,  and  has 
a  very  irritating  odor.     It  neither  burns  nor  supports  com- 
bustion ;  it  turns  blue  litmus  paper  red,  and  is  very  soluble 
in  water.     At  0°  C.  1  liter  of  water  will  dissolve  about  500 
liters  of  hydrochloric  acid  gas.     So  great  is  its  affinity  for 
moisture  that  whenever  it  escapes  into  damp  air,  heavy, 
white  clouds  appear. 

32.  The  commercial  acid,  which  is  simply  an  aqueous 
solution  of  the  gas,  contains  about  32  per  cent  of  acid. 
Very  dilute  solutions  of  hydrochloric  acid  may  be  concen- 
trated by  heating  until  the  solution  contains  20  per  cent 
of  acid,  but  the  process  can  be  carried  no  further.     On 
the  other  hand,  very  strong  acid,  if  exposed  to  the  air,  or 
if  heated,  loses  strength. 

33.  Hydrochloric  acid  has  great  affinity  for  ammonia ; 
if  a  bottle  of  hydrochloric  acid  and  a  bottle  of  ammonia 
remain   undisturbed   side   by   side   for   some   time,  they 
become  thickly  coated  about    the    top   with    ammonium 
chloride,  a  white  salt  formed  by  the  union  of  the  two 
gases. 

34.  Uses  of  Hydrochloric  Acid.  —  The  chief  use  of  this 
acid  is  in  the  preparation  of  chlorine  for  the  manufacture 
of  bleaching  powder.     It  is  also  used  very  largely  in  all 
chemical  laboratories  as  a  reagent,  in  gas  works  to  neu- 
tralize the  ammonia  solutions  drawn  off  from  the  "washer," 
and  in  the  preparation  of  various  chlorides. 


116  MODERN  CHEMISTRY 

BROMINE  :  Br  =  80 

35.  Where  found.  —  Because  of  its  great  chemical  activ- 
ity, bromine,  like  chlorine,   does  not  occur  free,  but  is 
found  in  sea  water  and  in  salt  wells  combined  with  sodium 
and  magnesium.     Its  discovery  dates  from  the  year  1826, 
when  Balard  found  it  in  sea  water. 

36.  Commercial  Supply.  —  The  greater  part  of  the  com- 
mercial supply  of  bromine  is  obtained  from  Germany  and 
the  United  States.      The   greater  amount  used   in   this 
country  comes  from  Pomeroy  Bend,  Ohio,  where  there  are 
a  large  number  of  salt  wells.     Bromine  appears  there  in 
the  form  of  magnesium  and  sodium  bromide.      The  salt 
water  from  these  wells  is  boiled  down  to  a  certain  extent, 
the  common  salt  (NaCl)  crystallizing  out,  while  the  other 
compounds  remain  in  solution.     This  residue  is  known  as 
the  "mother  liquor."     The  next  step  in  the  process  is  to 
put  the  solution  into  stills  hewn  out  of  solid  rock,  adding 
to  it  manganese  dioxide  and  sulphuric  acid.     The  whole 
is  then  heated  by  steam  introduced  into  the  liquid  through 
pipes.    Bromine  distills  over  and  is  condensed  under  water. 

37.  Formerly  bromine   was   expensive,   but,  owing  to 
cheaper  methods  of  production,  the  price  has  been  so  re- 
duced that  many  of  the  salt  works  no  longer  prepare  it. 
The  method  of  preparation  described  above  is  illustrated 
in  the  following  experiment :  — 

EXPERIMENT  76.  —  Into  a  test-tube  put  a  few  small  crystals  of 
sodium  or  potassium  bromide,  add  a  little  manganese  dioxide,  and 
cover  with  sulphuric  acid.  Warm  slightly  and  notice  the  dark  red 
gas  given  off.  What  other  gas  have  we  prepared  that  resembles  this 
somewhat?  Describe  the  odor.  How  does  it  affect  the  eyes?  Try 
its  bleaching  effects  upon  a  moistened  piece  of  calico  or  litmus  paper. 
How  does  it  compare  with  chlorine  in  this  respect?  Does  anything 
condense  upon  the  cooler  portion  of  the  tube?  What  is  its  physical 
condition  ?  Its  color  ? 


THE  HALOGENS  11? 

38.  Laboratory  Method  of  obtaining  Bromine.  — If  some 
bromine  is  desired  for  class  experiments,  it  may  be  pre- 
pared as  above.     Attach  a  delivery  tube  and  conduct  the 
gas  into  cold  water.     As  soon  as  the  water  is  saturated, 
the  bromine  will  condense  in  the  bottom  of  the  jar.     It 
may  then  be  obtained  from  the  water  by  a  separating 
funnel,  or  by  pouring  into  a  burette  and  drawing  off  the 
heavier  liquid  as  needed  for  experiment.     Preserve  both 
the  bromine  and  the  water. 

39.  The  reaction  that  takes  place  is  the  same  as  in  the 
preparation  of  chlorine  by  a  similar  method,  thus :  — 

2  KBr  +  2  H2SO4  +  MnO2  = 

K2SO4  +  MnSO4  +  2  H2O  +  Br2. 

40.  Another  Method.  —  Sometimes  another   method  is 
used  when  the  purpose  is  merely  to  determine  whether 
bromine  is  present  in  a  solution       In  this  process  the 
bromine   is   set   free  from  its  compound   by  the  use  of 
chlorine. 

EXPERIMENT  77. —  To  the  solution  supposed  to  contain  bromine 
add  a  little  chlorine  water  as  prepared  in  Experiment  61.  If  bromine 
is  present,  the  solution  should  turn  darker  in  color,  due  to  the  libera- 
tion of  the  bromine  by  the  chlorine.  Which  does  this  experiment 
show  to  have  the  greater  chemism  ?  To  prove  that  this  color  is  due 
to  the  presence  of  free  bromine  add  about  a  half  cubic  centimeter  of 
carbon  disulphide,  shake  well,  and  allow  it  to  settle.  If  free  bromine 
is  present,  the  disulphide  will  be  turned  brown  from  the  fact  that  it 
has  taken  up  all  the  free  bromine  in  the  solution. 

41.  Characteristics   of    Bromine. — Bromine   is   a   dark 
reddish  brown  liquid.     It  is  the  only  non-metallic  ele- 
ment that  is  a  liquid.     It  is  very  volatile,  giving  off  at 
all  temperatures  heavy  brown  fumes.     At  seven  degrees 
below  zero  it  solidifies.     It  has  a  very  disagreeable  odor, 


118  MODERN  CHEMISTRY 

and  attacks  not  only  the  throat  and  nostrils,  but  also  the 
eyes.  It  differs  from  chlorine  in  that  the  odor  is  more 
sickening,  and  it  was  this  fact  that  gave  to  the  element 
the  Greek  name  bromos,  meaning  offensive  odor. 

42.  The  vapors  are  non-combustible,  yet,  like  chlorine, 
they  allow  of  the  continued  combustion  of  a  jet  of  hydro- 
gen.    As  the  hydrogen  burns,  the  red  vapors  gradually 
disappear,  and  colorless  hydrobromic  acid  gas  takes  their 
place.     Powdered  arsenic,  sifted  into  the  vapors,  burns, 
and  a  small  bit  of  antimony  dropped  upon  liquid  bromine 
burns  brightly,  and  the  heat  generated  by  the  chemical 
action  melts  the  metal,  which  spins  around  upon  the  sur- 
face like  sodium  upon  water.      Bromine  is  soluble  to  a 
considerable  extent  in  water,  and  if  the  temperature  of 
such  a  solution  is  reduced  by  surrounding  it  with  a  freez- 
ing  mixture,   light    brown    crystals    of    bromine   hydrate 
separate,  as  did  the  crystals  of  chlorine  hydrate  under 
similar  circumstances. 

43.  Experiments  with  Bromine.  —  Let  the  teacher  prove 
the  above  facts  by  experiments  with  bromine  before  the 
class. 

EXPERIMENT  78.  —  Place  a  small  piece  of  phosphorus  in  a  defla- 
grating spoon  and  put  it  into  a  jar  of  bromine  vapor.  Allow  it  to 
remain  a  few  minutes.  Does  it  burn?  Compare  bromine  with  chlo- 
rine in  this  regard. 

EXPERIMENT  79.  —  To  test  the  bleaching  effects  of  bromine  upon 
colored  solutions.  Pour  into  a  bottle  a  little  bromine  vapor,  and  add 
a  few  cubic  centimeters  of  logwood,  litmus,  or  carmine  solution.  Shake 
it  up.  Notice  the  effect  upon  the  color. 

44.  Uses  of  Bromine.  —  The  principal  use  of  bromine  is 
as  a  disinfectant.     It  is  also  used  in  organic  work  in  chem- 
istry and  in  the  preparation  of  some  dyes.     For  organic 
colors  it  is  a  strong  bleaching  agent,  though  not  as  active 


THE  HALOGENS  119 

as  chlorine.  There  are  also  several  compounds  which 
have  application  in  medicine.  Of  these  magnesium  bro- 
mide, MgBr2,  and  potassium  bromide,  KBr,  are  the  most 
important;  the  former  is  found  in  the  water  of  many 
mineral  springs  and  is  regarded  as  of  medicinal  value ; 
the  latter  is  used  as  a  sedative  in  the  case  of  nervous 
headache.  A  third  compound,  silver  bromide,  AgBr,  is 
used  in  photography  for  sensitizing  various  printing 

papers, 
j/  IODINE  :  1  =  127 

*45.  The  Source  of  Supply.  —  Until  within  recent  years, 
the  iodine  of  commerce  was  obtained  from  certain  varieties 
of  sea-weeds.  These  weeds  were  collected  in  large  quan- 
tities and  burned,  and  the  ashes  treated  with  water  to 
dissolve  out  the  sodium  carbonate  which  was  wanted  for 
making  soap.  If  such  sea- weeds  are  burned  at  a  low  tem- 
perature, the  iodine  will  remain  in  the  ashes  in  the  form 
of  sodium  and  potassium  iodide.  From  these  it  can  be 
obtained  as  shown  below. 

46.  The  greater  part  of  our  present  supply  of  iodine 
comes  from   Chile.      There  is  a  desert  in  that  country 
many  square  miles  in  area,  where  are  found  vast  deposits 
of  sodium  nitrate  mixed  with  considerable  quantities  of 
soil  and  small  amounts  of  iodine  compounds.     This  mix- 
ture is  treated  with  water,  which  dissolves  out  the  sodium 
nitrate  and  the  iodates;  the  solution  is  then  evaporated 
till  the  sodium  nitrate  crystallizes  out,  as  in  the  manufac- 
ture of  bromine  in  Ohio,  leaving  the  iodine  compounds 
still  in  solution.     The  residual  solution,  called  the  "  mother 
liquor,"  is  treated  with  manganese  dioxide  and  sulphuric 
acid,  and  gently  heated. 

47.  Preparation  for  Commerce.  —  When  treated  as  above, 
from  the  mother  liquor,  violet  fumes  of  vaporous  iodine 


120  MODERN  CHEMISTRY 

are  given  off  abundantly ;  they  are  passed  over  into  cool 
chambers,  where  they  condense.  To  further  purify  the 
iodine,  it  is  resublimed  at  a  low  temperature  and  con- 
densed in  a  series  of  conical-shaped  flasks  (see  Fig.  36). 


FIG.  36.  —  Iodine  Apparatus. 


At  the  left  is  a  small  brick  furnace,  in  the  upper  part  of 
which  is  an  oven.  The  iodine  to  be  purified  is  placed  in 
the  oven,  and  gently  heated.  The  final  reaction  in  the 
separation  of  the  iodine  is  the  same  as  in  the  case  of  the 
bromine  and  chlorine. 


2  NaI  +  2  H2SO4+MnO2=Na2SO4  +  MnSO4+2  H2O  +  I2. 

The  essential  features  of  this  method  of  preparing  iodine 
may  be  shown  by  the  following  experiment  :  — 

EXPERIMENT  80.  —  Into  a  small  test-tube  put  a  crystal  or  two  of 
potassium  iodide,  add  a  little  manganese  dioxide,  and  cover  with  sul- 
phuric acid.  Warm  gently  ;  notice  the  fumes  that  are  given  off  and 
what  condenses  upon  the  cooler  portion  of  the  tube. 

48.  Another  Method  of  preparing  Iodine.  —  The  follow- 
ing method  is  employed  to  some  extent  in  France  in 
obtaining  iodine  from  the  ashes  of  sea-weeds.  It  is  also 
the  usual  method  pursued  in  the  laboratory  in  testing  for 
iodine.  The  plan  consists  simply  in  adding  free  chlorine 


THE  HALOGENS  121 

to  the  iodine  solution,  whereby  the  latter  is  liberated  from 
its  compounds.  As  a  commercial  method  it  is  open  to  the 
objection  that  if  too  little  chlorine  is  added,  not  all  of 
the  iodine  is  liberated,  and  if  too  much,  a  portion  com- 
bines with  the  chlorine. 

EXPERIMENT  81.  —  To  a  solution  containing  iodine  in  combina- 
tion add  a  few  drops  of  chlorine  water.  What  change  in  color  takes 
place  ?  This  indicates  free  iodine,  as  may  be  proven  by  adding  starch 
paste  solution.  The  starch  will  turn  blue,  as  it  did  with  ozone. 

49.  Experiments  with  Iodine.  —  Many  characteristics  of 
iodine  may  be  learned  from  the  following  experiment  :  — 

EXPERIMENT  82. — Put  a  small  crystal  of  iodine  into  a  test-tube 
and  warm  gently.  What  happens?  Describe  the  color  and  odor  of 
the  vapors.  Hold  a  piece  of  moistened  starch  paper  near  the  mouth 
of  the  test-tube  ;  how  is  the  starch  affected  ?  Close  the  mouth  of  the 
tube  with  your  finger  and  notice  the  stain  that  is  formed.  See  whether 
you  can  remove  it  by  moistening  with  caustic  potash  or  ammonia. 

50.  Characteristics  of  Iodine.  —  Iodine  is  a  solid  of  a 
dark  bluish  black  color,  with  a  metallic  luster.      At  or- 
dinary temperatures  it  is  somewhat  volatile,  and  when 
gently  heated  it  is  readily  converted  into  vapors  of  a 
beautiful  violet  color.      It  was  from  this  fact  that  the 
element  received  its  name,  iodine  being  derived  from  a 
Greek  word  which  means  violet.     The  odor  of  the  vapors 
resembles  somewhat  that  of  dilute  chlorine,  but  is  less 
irritating.     It  has  the  power  of  turning  the  skin  yellow, 
but  the  stain  may  be  removed  by  treatment  with  some 
alkali.      It   has   feeble   bleaching   properties,    and    turns 
starch  paste  blue.     This  is  so  delicate  a  test  that  one 
part  of  iodine  in  several  hundred  thousand  of  water  will 
be  clearly  shown.     Its  affinity  for  phosphorus  is  so  strong 
that  if  a  crystal  of  iodine  be  dropped  upon  a  small  piece  of 
phosphorus,  the  latter  will  be  ignited  almost  instantly. 


122  MODERN  CHEMISTRY 

51.  Solvents  for  Iodine.  —  Among  the  better  solvents 
for  iodine  are  chloroform,   ether,   alcohol,   carbon  disul- 
phide,  and  a  solution  of  potassium  iodide. 

EXPERIMENT  83.  —  Put  a  crystal  of  iodine  into  a  test-tube  with  a 
little  cold  water.  Shake  for  a  moment  or  two,  and  then  pour  off  a 
part  of  it  into  another  tube  and  test  with  starch  paste  to  determine 
whether  any  has  dissolved.  What  are  your  conclusions?  Warm  the 
remainder;  what  indications  are  there  that  the  iodine  is  dissolving? 
Test  the  solution  again  with  starch  paste,  or  with  carbon  disulphide, 
thus  :  add  about  a  half  cubic  centimeter  of  the  disulphide  to  the  iodine 
solution,  and  shake  well.  Notice  the  beautiful  violet  color  imparted 
to  the  disulphide. 

Try  alcohol  also  as  a  solvent.  Before  testing  the  solution  with 
starch  or  carbon  disulphide,  dilute  until  pale  yellow  in  color.  What 
are  the  results?  Try  in  the  same  way  a  solution  of  potassium  iodide 
upon  an  iodine  crystal,  and  state  results. 

52.  Uses  for  Iodine.  —  In  the  form  of   a  tincture,  or 
alcoholic  solution,  iodine  is  used  to  a  considerable  extent 
in  medicine  to  prevent  the  spread  of  eruptive  diseases,  like 
erysipelas,  in  skin  affections,  sore  throat,  and  the  like.     In 
the  compound  iodoform  it  is  used  by  physicians  as  a  deo- 
dorant and  disinfectant.     As  potassium  or  sodium  iodide 
it  is  frequently  used  as  a  reagent  in  the  laboratory,  and 
to  a  limited  extent  in  making  aniline  dyes.     In  these  vari- 
ous ways  300  tons  or  more  are  used  annually. 

53.  Some  Comparisons.  —  It  has  probably  been  observed 
that  the  same  method  is  used  in  preparing  chlorine,  bro- 
mine, and  iodine.     Notice  the  following  reactions :  — 


Cl 


Br 


MnO2  +  2  H2SO4  +  2NaCl  =  MnSO4  +  Na2SO4 
+  2  H20  +  C12. 


MnO2  +  2H2SO4  +  ZNaBr  =  MnSO4  +  Na2SO4 


2  H20 


=  MnSO4 
2H0+/. 


THE  HALOGENS  123 

SUMMARY  ©F  CHAPTER 

Meaning  of  term  halogen. 

Names,  symbols,  and  atomic  weights  of  the  halogens. 

Comparison  of  the  halogens. 

a.  Method  of  preparing. 

b.  Physical  condition  at  ordinary  temperatures;  at  lower  tem- 

peratures. 

c.  Color. 

d.  Odor. 

e.  Density. 

/.    Chemical  activity. 

g.   Bleaching  powers. 

h.   Affinity  for  certain  substances,  as  hydrogen,  phosphorus,  etc. 

{.    Uses. 

j.    Hydrogen  compounds. 

Compare  hydrofluoric  and  hydrochloric  acids  as  to  — 

1.  Method  of  preparation. 

2.  Characteristics. 

3.  Uses. 
Special  points  for  study. 

Method  of  etching  glass. 

What  kind  of  substances  may  be  used  instead  of  manganese 
dioxide  in  preparing  chlorine?     Why? 

Proof  of  this  by  experiments. 

Practical  application  of  this. 
Compare  these  two  methods  of  making  chlorine :  — 

1.  MnO2  +  HCL 

2.  MuO2  +  XaCl  +  H2SO4. 

How  similar  ?     How  different  ? 
Explain  how  chlorine  bleaches.     Write  the  equation.     Source  of 

commercial  supply  of  hydrochloric  acid. 
Tests  for  bromine  and  iodine  with  carbon  disulphide  —  compare 

results. 

Method  of  obtaining  and  purifying  iodine. 
Describe  experiments  which  illustrate  chief  properties  of  chlorine, 

bromine,  and  iodine. 
Solvents  for  chlorine,  bromine,  and  iodine. 


CHAPTER  X 

ACIDS,   ALKALIES,  AND  SALTS 

1.  Neutralization.  — There  are  a  great  many  substances 
which,  if  put  together,  have  the  power  of  destroying  the 
characteristic  properties  of  each  other. 

EXPERIMENT  84.  —  To  show  this  fact,  put  into  an  evaporating  dish 
about  10  cc.  of  dilute  hydrochloric  acid  and  dip  into  it  a  small  piece 
of  blue  litmus  paper.  Notice  that  it  is  changed  to  red.  Now  add 
slowly,  stirring  all  the  time  with  a  glass  rod,  a  solution  of  caustic 
soda,  until  the  litmus  paper  just  turns  blue  again;  then  add  one  drop 
of  hydrochloric  acid.  You  ought  now  to  have  a  solution  that  will  not 
affect  either  red  or  blue  litmus  paper.  Boil  this  solution  to  dryness. 
What  is  the  appearance  of  the  solid  thus  obtained?  Taste  it.  Does 
it  seem  familiar  ?  Dissolve  it  in  a  little  water  and  test  with  both  red 
and  blue  litmus  paper.  Is  the  paper  affected?  Now  boil  a  little 
hydrochloric  acid  to  dryness.  Does  it  leave  a  residue?  Examine  a 
specimen  of  solid  caustic  soda  and  compare  with  the  white  solid 
obtained  above.  Are  the  two  solids  the  same?  Do  they  both  affect 
litmus  in  the  same  way  ? 

2.  From  this  experiment  we  see  that  the  acid  and  the 
caustic  soda,  on  being  put  together,  have  both  lost  their 
characteristic  properties  and  have  reacted  to  form  a  new 
substance  having  the   properties   of   neither.      In   other 
words,  they  have  neutralized  each  other. 

3.  Bases.  —  Such  substances  as  have  the  power  of  neu- 
tralizing  the  properties  of  acids  are  called  bases.     This  was 
shown  in  Experiment  84  above.     We  have  already  seen 
that  the  compound  of  any  element  with  oxygen  is  called 
an  oxide;  many  of  the  oxides  combine  with  water  to  form 

124 


ACIDS,  ALKALIES,  AND  SALTS  125 

zvater  oxides,  or,  to  use  the  ordinary  term,  which  is  from 
the  Greek,  hydroxides  or  hydrates.  We  have  seen  also 
that  some  oxides  or  anhydrides,  when  united  with  water, 
form  acids,  as,  for  example,  nitrogen  trioxide.  Strictly 
speaking,  such  compounds  are  hydroxides,  but  we  never 
apply  that  term  to  them  ;  it  is  restricted  to  the  compounds 
of  metallic  oxides  with  water.  In  brief,  bases  are  metallic 
hydroxides. 

~Ty%"  Alkalies.  —  Bases,  soluble  in  water,  which  have  ex- 
-  ceedingly  strong  basic  properties,  are  called  alkalies.  The 
four  most  common  alkalies  are  the  three  hydroxides  of 
sodium,  potassium  and  calcium,  and  ammonia.  If  we 
study  the  'formulae  of  the  hydroxides,  we  shall  see  that 
water  may  be  taken  as  the  type  upon  which  all  the  others 
are  built.  Thus  :  — 

Water HOH 

Caustic  Potash  .     .     ,     .     .     .  KOH 

Caustic  Soda NaOH 

Lime  Water     -. Ca(OH)2 

Ammonium  Hydroxide    .     .     .  NH4OH 

The  only  difference  is  that  one  atom  of  hydrogen  in  the 
water  has  been  replaced  by  some  metal  or  group  of  elements. 

5.  As  most  of  the  metals  themselves  have  certain 
characteristic  properties  of  bases,  they  are,  by  some, 
spoken  of  as  bases.  Possibly  there  is  no  serious  objec- 
tion to  this,  but  it  should  be  remembered  that  all  bases 
are  compounds ;  thus,  sodium  may  have  many  of  the 
properties  of  a  base,  but  it  is  not  a  base  any  more  than 
bromine  is  an  acid. 

§.  Acids.  —  It  is  a  difficult  matter  to  define  acids.  They 
are  substances  which  have  certain  properties  the  opposite 
of  bases.  They  possess  the  power  not  only  of  turning 


126  MODERN  CHEMISTRY 

blue  litmus  red,  but  of  similarly  affecting  various  other 
vegetable  colors,  all  of  which  are  restored  again  by  the 
use  of  an  alkali.  They  also  have  a  sour  taste,  though 
this  is  not  a  distinctive  feature,  as  many  bodies  not  acids 
also  have  the  same  property. 

7.  Their  Composition.  —  If  we  recall  the  formulae  of  the 
few  acids  we  have  already  used,  nitric,  hydrochloric,  and 
sulphuric,  we  see  that  they  all  contain  hydrogen ;    it  is 
true  also  that  most  contain  oxygen,  together  with  some 
third  element  which  seems  to  give  the  distinctive  proper- 
ties to  the  acid.      It  was  at  one  time  supposed  that  all 
acids  contained  oxygen,  and  in  accordance  with  this  idea 
oxygen  received  its  name.     Later,  however,  were  discov- 
ered hydrochloric  and  other  acids,   which  contained  no 
oxygen  whatever.     A  distinctive  property  of  acids  is  that 
they  all  have  the  power  of  giving  up  the  whole  or  a  part 
of  their  hydrogen,  and  of  combining  instead  with  some 
metal  or  base.     This  we  have  seen.    They  are  compounds 
of  water  with  non-metallic  oxides,  and  sometimes  their 
formulae  are  written  as  if  they  were  hydroxides;   thus, 
H2S04,  S02(OH)2;  HN03,  NO2(OH),  etc. 

8.  Salts.  —  A  salt  is  a  compound  formed  by  the  union 
of  an  acid  with  a  base  or  metal,  possessing  properties 
different  from  those  of  either  of   its  constituents.      We 
have  been  accustomed  to  think  of  salt  as  a  particular  sub- 
stance used  in  seasoning  food,  but  we  must  now  remember 
that  it  is  a  term  applied  to  a  large  number  of  compounds, 
called  salts  because  they  resemble  common  salt  in  appear- 
ance or  properties.     They  are  all  produced  in  the  same 
way.      We  saw  above  that  when  we  neutralized  hydro- 
chloric acid  with  caustic  soda  and  boiled  to  dry  ness,  we 
obtained  a  white  solid,  resembling  and  tasting  like  com- 
mon salt,  which  it  really  was. 


ACIDS,  ALKALIES,  AND  SALTS  127 

EXPERIMENT  85.  —  In  the  same  way  as  in  Experiment  84,  neu- 
tralize about  10  cc.  of  hydrochloric  acid  with  caustic  potash  and  boil 
to  dryness  as  before.  Compare  the  salt  produced,  in  taste  and  appear- 
ance, with  that  obtained  before. 

9.  Normal  or  Neutral  Salts. — There  are  two  general 
classes  of  salts,  neutral  or  normal,  and  acid.  A  normal 
salt  is  one  in  which  all  the  displaceable  hydrogen  of  the 
acid  used  in  making  the  salt  has  been  replaced  by  some 
base.  For  example,  when  caustic  potash  and  sulphuric 
acid  neutralize  one  another,  the  following  reaction  takes 
place  :  — 

H2SO4  +  2  KOH  =  K2SO4  +  2  H2O. 

We  see  here  that  all  the  hydrogen  in  the  sulphuric  acid, 
two  atoms,  has  been  replaced  by  an  equivalent  amount  of 
the  metal,  potassium,  and  the  salt  produced,  potassium 
sulphate,  K2SO4,  is  a  normal  salt. 

10.  Again,  if  lead  is  treated  with  vinegar  (acetic  acid), 
which  is  represented  by  the  formula  HC2H3O2,  we  have 
this  reaction :  — 

Pb  +  2  HC2H302  =  Pb(C2H302)2  +  H2. 

It  will  be  noticed  that  in  the  salt  resulting,  Pb(C2H3O2)2, 
a  quantity  of  hydrogen  remains.  Lead  acetate  is,  notwith- 
standing, a  neutral  salt,  because  only  one  atom  of  hydro- 
gen, the  first,  in  each  molecule  of  acid  can  be  displaced. 

11.  Acid   Salts. — If,  however,  we  use   only  half  the 
amount  of  caustic  potash  shown  by  the  first  reaction  above 
with  the  sulphuric  acid,  we  shall  replace  only  half  of  the 
hydrogen  in  the  acid,  and  the  salt  resulting  will  be  an 
acid  salt,  thus  :  — 

H2SO4  +  KOH  =  KHSO4  +  H2O. 


128  MODERN  CHEMISTRY 

12.  Reading  the  Formulae  of  Salts.  —  The  compound, 
K2SO4,    is   read,    normal  potassium   sulphate,    or   usually, 
simply  potassium  sulphate.     The  acid  salt,  KHSO4,  is  read, 
acid  potassium  sulphate,  or  potassium  hydrogen  sulphate. 
Sometimes  the  prefix  mono  is  applied,  but  usually  only  in 
the  case  of  salts  of  acids  having  three  or  more  replacealle 
hydrogen  atoms,  as  phosphoric,  H3PO4,  or  silicic,  H4SiO4 
With  these  acids  we  may  form  the  following  salts :  — 

Phosphoric  Acid,  H3PO4 

Mono-sodium  Phosphate NaH2PO4 

Di-sodium  Phosphate Na2HPO4 

Normal  sodium  Phosphate Na3PO4 

Silicic  Acid,  H4SiO4 

Mono-sodium  Silicate NaH3SiO4 

Di-sodium  Silicate  ....  ...  Na2H2SiO4 

Tri-sodium  Silicate Na3HSiO4 

Normal  sodium  Silicate Na4SiO4 

EXERCISES. — In  the  following  formulae,  state  which  represent 
acids,  which  bases,  and  which  salts,  giving  reasons  therefor.  Give 
also  the  name  of  the  substance  'represented.  If  salt,  state  whether 
acid  or  normal :  — 

Na2S04,  KOH,  H2SO4,  P(OH)3,  ZnSO4,  KNO3,  Ca(OH)2,  BaSO4, 
K3P04,  K2HP04,  KH2P04,  HC1,  NaOH,  NaHSO4,  NaNO3. 

13.  Nomenclature  of  Acids.  —  It  will  be  noticed  that 
with  one  exception  the  acids  we  have  met  with  so  far  all 
have  names  ending  in  ic  ;  thus  :  — 

Sulphuric     ....  H2SO4 

Nitric HNO3 

Phosphoric  ....  H3PO4 

Silicic      .....  H4SiO4,  etc. 


Sulphur           : 

acid,    H2SO4  . 

Sulphuric 

Nitrogen         : 

HNO3   . 

.     Nitric 

Phosphorus     : 

H3P04  . 

.     Phosphoric 

Silicon             : 

H4SiO4. 

Silicic 

ACIDS,   ALKALIES,  AND  SALTS  129 

The  greater  number  of  acids  with  which  we  shall  have 
to  deal,  as  already  stated,  contain  three  elements,  the  first 
of  which  is  hydrogen,  the  third  oxygen,  and  a  second 
which  gives  the  name  to  the  acid.  Thus  the  middle  sym- 
bols in  the  above  formulas  are  :  — 

S  . 

N  . 

P  . 

Si  . 

14.  Sometimes,    however,   this   second   element    forms 
more  than  one  acid  with  hydrogen  and  oxygen.     In  such 
cases  the  most  common,  and   hence  the  earliest   known, 
received  the  name  with  the  termination  ic.      Then  the 
acid  having  a  smaller  amount  of   oxygen   is   given,  the 
termination  ous.     This  we  have  seen  in  the  two  nitro- 
gen acids :  — 

Nitric  .     .     .     HNO3     .     .     Oxygen,  3  atoms. 
Nitrous     .     .     HNO2     .     .  2      " 

15.  Sometimes  even  three  or  four  acids  are  formed  from 
the  same  three  elements,  the  amount  of  oxygen  only  vary- 
ing.    In  such  cases,  the  one  with  the  least  quantity  of 
oxygen  is  given  the  prefix  hypo,  meaning  under  or  lesser, 
and  the  one  with   the  most  oxygen  has  the  prefix  per, 
beyond  or  above.     These  may  be  illustrated  by  the  follow- 
ing series :  — 


Sulphured  .  *  r  5  ,  H2 
Sulphurous.  .  .  .  H2 
.  H 


O4     .     .     Oxygen,  4  atoms 
O3     .     .          "          3     " 
O0  "2     " 


130  MODERN   CHEMISTRY 


CHLORINE  ACIDS 


Perchloric  .     H 

Chloric     .     .     .     H 
Chlorous  H 


Cl 
Cl 
01 


O4     .     .     Oxygen,  4  atoms. 
O3     .     .  "         3      " 

Oo  "         2      « 


Hypo-chlorous    .     .     H   Cl  O      .     .  "         1      " 

16.  Nomenclature  of  Salts.  —  All  of  the  acids  named 
above  have  the  power  of  combining  with  various  metals, 
or  their  hydroxides,  to  form  salts.     All  such  as  result 
from  the  union  of  a  base  with  an  ic  acid  are  given  names 
with  the  "termination  ate.      Thus,  all  salts  of  sulphuric 
acid  are  sulphates;  of  nitric  acid,  nitrates;  phosphoric  acid, 
phosphates,  etc.     To  illustrate  :  — 

H2SO4,  sulphuric  acid,  gives — 

with  zinc,  ZnSO4,  zinc  sulphate  ; 
with  potassium,  K2SO4,  potassium  sulphate  ; 
.   with  calcium,  CaSO4,  calcium  sulphate. 

HNO3,  nitric  acid,  gives  — 

with  potassium,  KNO3,  potassium  nitrate  ; 
with  sodium,  NaNO3,  sodium  nitrate ; 
with  ammonia,  NH4NO3,  ammonium  nitrate. 

17.  Salts  formed  from  the  ous  acids  receive  names  end- 
ing in  ite.     (It  may  aid  the  memory  in  associating  the 
pronouns  singular,  J,  plural  objective  us,  with  the  ous 
acids  and  ite  salts.)     Thus,  from 

H2SO3,  sulphurous  acid,  we  have 
K2SO3,  potassium  sulphite  ; 
Na2SO3,  sodium  sulphite,  etc. 


ACIDS,  ALKALIES,  AND  SALTS  131 

In  the  case  of  salts  formed  from  the  hypo  and  per 
acids,  the  corresponding  prefix  is  simply  given  to  the 
salt.  Thus  :  - 

NaCIO,  sodium  hypochlorite,  from 
HC1O,  acid,  %p0chlorous,  and 
NaClO4,  sodium  perddorate,  from 
HC1O4,  acid,  perchloric. 

18.  Binary  Compounds.  —  All  of  the  above  salts  are 
formed  from  what  are  sometimes  called  ternary  acids; 
that  is,  those  consisting  of  three  (or  more)  terms.  In 
like  manner,  a  binary  compound  would  be  one  which 
consists  of  only  two  elements.  The  following  are  ex- 
amples :  — 

Common  Salt       ....     NaCl 
Calcium  Chloride     .     .     . 


Water  .......     H2O 


Turpentine 


It  will  be  noticed  from  these  formulae  that  though  in  a 
binary  compound  there  are  but  two  elements,  the  number 
of  atoms  of  each  of  these  elements  is  quite  variable. 

19.  As  already  stated,  there  are  a  few  acids  which 
contain  no  oxygen.  Salts  obtained  from  them  would, 
therefore,  all  be  binaries.  Thus  :  — 

from  Hydrochloric      acid,  HC1,  we  obtain  the  chlorides  ; 
Hydrobromic         "     HBr,  "  bromides; 

Hydriodic  "     HI,  "  iodides; 

Hydrofluoric         "     HF,  "  fluorides; 

Hydrosulphuric    "     H2S,  *;  sulphides. 


132  MODERN  CHEMISTRY 

20.  How  Binary  Compounds  are  Named.  —  It  will  be 
noticed  that  all  binary  salts  are  given  names  ending  in 
ide.     Furthermore,  it  is  seen  that  it  is  the  negative  ele- 
ment in  every  case  which  gives  the  name  to  the  substance ; 
thus :  — 

NaCl   ^| 

KOI 

-,,,-,    \-  are  all  chlorides,  while  the  positive 

MnCl2  I 

CaCl2  J 

element  indicated  in  the  formula  is  simply  descriptive  in 
character,  or  the  adjective  that  tells  what  kind  of  a 
chloride.  Thus  the  above  are 

Sodium 

Potassium      „, .     . , 
TV*  \  Chloride ; 

Manganese 

Calcium 

just  as  we  might  say 

Stone 

Brick 

„  [  House. 

Frame 

Log 

21.  It  frequently  happens  that  two  elements,  just  as  in 
the  case  of  the  ternary  acids,  may  unite  in  different  pro- 
portions  to   form   two   or  more  compounds.      We  have 
already  seen  this  in  studying  the  oxides  of  nitrogen,  p.  81. 
When   two  such  exist,  as   for   example  the  two  oxides 
of  mercury,  HgO  and  Hg2O,  the  one  having  the  smaller 
proportion  of  the  negative   element,  as  indicated  by  the 
formula,  is  the  ous  compound,  just  as  in  the  case  of  the 
acids  already  studied,  while  the  one  having  the  greater 
proportion  of  the  same  element  is  the  ic  compound. 


ACIDS,  ALKALIES,  AND  SALTS  133 

22.  Again,  we  noticed  in  studying  the  oxides  of  n> 
trogen  :  — 

N2O,  ratio  of  oxygen  to  nitrogen,  1  : 2 

N202,     "  "         2:2  =  1:1. 

Jn  the  first  we  found  one-half  as  many  atoms  of  oxygen  as 
of  nitrogen  ;  in  the  second  the  same  number  ;  they  were 
therefore  called  nitrons  and  nitric  oxides.  In  a  few 
instances,  instead  of  using  the  English  name  with 
the  terminations  ous  and  ic,  for  the  sake  of  euphony, 
the  Latin  forms  are  taken.  Thus  :  — 

Cu2O,    Cuprous  Oxide 
CuO,     Cupric         " 
FeCl2,    Ferrous  Chloride 
Fe2Cl6,  Ferric 

23.  Returning  to  the  series  of  nitrogen  compounds,  it 
will  be  noticed  that  they  were  given  two  names.     This  is 
very  often  done,  one  of  them  using  a  prefix  to  indicate 
the  exact  number  of  atoms  of  the  last  element  in  the 
formula  of  the  compound.     Thus  we  have 

N2O,  Nitrogen  Monoxide. 
N2O4,  "  Tetroxide 
P2O5,  Phosphorus  Pentoxide,  etc. 

24.  Old  Forms.  —  Occasionally  we  use  the  old  terms, 
pro,  per,  and  sesqui.     The  first  is  a  prefix,  meaning  before, 
and  is  given  to  some  uncommon  or  unstable  compounds 
which  in  the  case  of  a  series  would  be  the  first  or  lowest. 
Thus,   FeO  is  sometimes   spoken    of   as   iron  protoxide. 
Nitrogen  tetroxide,  N2O4,  is   also  called  peroxide,  as  is 


134  MODERN  CHEMISTRY 

hydrogen  dioxide  as  well,  it  being  the  compound  com- 
ing in  the  series  beyond  the  others.  Sesqui  is  applied 
to  binary  compounds  in  which  the  two  elements  unite 
in  the  ratio  of  2  to  3,  as  in  Fe2O3,  iron  sesquioxide. 

SUMMARY   OF  CHAPTER 

Neutralization  —  Meaning  of  the  term. 

Experiments  to  illustrate. 
Three  classes  of  compounds. 
Compare  bases  and  acids. 

a.  In  composition. 

b.  In  properties. 
Alkalies  —  What  are  they  ? 

Examples. 

Salts  —  What  are  they  ? 
Two  classes. 

How  formed. 

How  distinguished  by  name. 

Examples  to  illustrate. 
Nomenclature. 

a.  Of  acids. 

b.  Of  salts. 
Examples  to  illustrate  both. 

Binary  compounds. 

Meaning  of  term  —  Illustrations. 
Six  important  classes  —  Examples. 
Nomenclature  —  Compare  with  acids. 


CHAPTER  XI 

CARBON  AND  A  FEW  COMPOUNDS.    C  =  12 

1.  Abundance.  —  With  the  exception  of  oxygen,  carbon 
is  the  most  widely  distributed  element,  and  is  also  very 
abundant.     In  the  form  of  compounds  it  is  found  in  the 
air  as   carbon   dioxide,   resulting   from   combustion   and 
respiration,  and  in  limestone,  CaCO3,  which  constitutes  a 
large  portion  of  the  rocky  crust  of  the  earth.     It  also 
occurs  in  almost  all  food  products,  such  as  sugar,  flour, 
starch,  vegetables,  and  fruits,  and  forms  a  large  part  of 
the  woody  structure  of  plants  and  trees. 

2.  Forms.  —  In  the  free  state  carbon  may  be  considered 
under  two  divisions  :  — 

a.  Crystallized,  including 

1.  The  Diamond. 

2.  Graphite  or  Plumbago. 

b.  Amorphous  (without  crystalline  form), 

1.  Coal. 

2.  Lampblack. 

3.  Gas  Carbon,  etc. 

3.  Diamonds.  —  The  diamond  occurs  in  octahedral  crys- 
tals.    It  is  found  in  South  America,  Africa,  Australia,  and 
India.     By  some  the  stones  are  thought  to  be  of  meteoric 
origin  and  not  native  to  the  earth,  but  the  theory  seems 
not  well  founded.     Moissan,  the  French  chemist,  has  suc- 
ceeded in  making  a  few  diamonds  in  the  electrical  furnace, 


136  MODERN  CHEMISTRY 

but  they  have  all  been  exceedingly  small,  and  black  in 
color,  so  as  to  have  no  value  except  in  a  scientific  way. 
In  nature  they  occur  rough  and  covered  with  a  layer  of 
partially  decomposed  rock.  The  most  highly  prized  are 
perfectly  transparent,  but  many  of  various  colors  have 
been  found.  The  diamond  has  strong  refractive  power, 
is  the  hardest  of  all  minerals,  and  can  be  cut  and  polished 
only  by  its  own  dnst. 

4.  Their  Practical  Uses.  —  Diamonds  are  used,  not  only 
as  ornaments,  but  also  in  cutting  glass ;  and  the  cheaper, 
imperfect  varieties  are  employed  as  tips  on  drills  for  cut- 
ting through  hard  rocks.     That  the  diamond  consists  of 
carbon  may  be  proved  by  burning  it  between  electric  ter- 
minals in   an   atmosphere   of  oxygen  ;    the  diamond  and 
oxygen  disappear,  and  carbon  dioxide,  CO2,  remains. 

5.  Graphite.  —  Next  to  the  diamond,  graphite  or  plum- 
bago is  the  purest  form  of  carbon.     It  is  sometimes  called 
black  lead,  but  it  contains  no  lead  whatever.     It  is  often 
found  in  hexagonal  prisms,  is  steel-gray  in  color,  has  a 
greasy  feeling,  and  as  a  mass  is  comparatively  soft,  though 
the  particles  themselves  are  very  hard. 

6.  That  it  consists  of  carbon  may  be  proved  by  testing 
it  in  the  electric  furnace,  as  in  the  case  of  the  diamond, 
similar  results  being  obtained. 

7.  Uses. — The   most   common   use   of   graphite  is  in 
making  what  are  known  as  lead  pencils,  so  named  because 
plumbago  was  at  first  supposed  to  be  a  compound  of  lead. 
In  making  pencils  the  graphite  is  thoroughly  pulverized 
and  mixed,  according  to  the  grade  of  pencil,  with  different 
proportions  of  fine  clay,  also  well  ground.     The  whole  is 
then  made  up  with  water  into  a  dough  and  pressed  into 
moulds  and  dried,  or  while  still  soft  is  forced  through 
plates  with  apertures  the  size  of  the  lead  in  the  pencil. 


CARBON  AND  A  FEW  COMPOUNDS       137 

Graphite  is  also  used  as  a  lubricant,  as  a  stove  polish,  and 
in  making  crucibles. 

8.  Amorphous  Carbon.  —  The  most  important  uncrys- 
tallized  forms  of  carbon  are  the  various  coals,  —  anthra- 
cite, semi-anthracite,  bituminous,  lignite,  peat,  jet,  cannel, 
and  the  artificial  form,  charcoal.      Of  great  importance 
also  are  gas  carbon,  lampblack,  and  coke. 

9.  Coal.  —  Coal  is  supposed  to  be  the  result  of  pressure 
and  heat  applied  to  a  luxuriant  vegetable  growth  in  the 
presence  of  moisture.      Peat  is  the  newest  of  the  coals, 
being  in  process  of  formation  in  swamp-lands  to-day.     It 
consists  almost  entirely  of  a  mass  of  roots.     Next  in  age 
is  lignite,  in  which  the  woody  structure  is  still  apparent. 

10.  Anthracite  and  Bituminous  Coals.  —  Anthracite  dif- 
fers from  bituminous  coal  in  that  the  former,  being  sub- 
jected to  greater  heat  and  pressure,  has  been  deprived  of 
its  volatile  products.     These  furnish  in  part,  at  least,  the 
petroleum  and  natural  gas  of  the  present  time.     Petroleum 
is  really  a  mixture  of  a  number  of  different  oils,  with  boil- 
ing points  differing  greatly.     These,  in  the  process  of  re- 
fining the  crude  oil,  distill  over  at  different  temperatures. 
Such  light  oils  as  naphtha  and  benzine  are  obtained  at  a 
low  temperature,  a  somewhat  higher  temperature  produc- 
ing kerosene,  and  higher  still  parafnne.     This  method  of 
separating  substances  through  differences  in  their  boiling 
points  is  called  fractional  distillation,  while  that  "in  which 
the  substance  heated  is  decomposed  is  called  destructive 
distillation. 

11.  Charcoal.  —  Charcoal,  because  of  the  abundance  of 
timber,  has  usually  been  prepared  in  a  simple,  but  very 
wasteful,  manner.     Large  piles  of  wood  are  covered  with 
earth  and  set  on  fire.     Most  of  the  air  is  excluded  in  this 
way,  and  only  enough  heat  is  produced  to  expel  the  vola- 


138 


MODERN  CHEMISTRY 


tile  products  from  the  wood.  At  present,  however,  in 
some  sections  the  wood  is  heated  in  iron  retorts,  and  the 
volatile  products  are  condensed  and  refined,  much  in  the 
same  way  as  with  petroleum. 

12.  Coke.  —  Coke  bears  the  same  relation  to  soft  or 
bituminous  coal  that  charcoal  does  to  wood.  It  is  an 
artificial  product  obtained  by  expelling  all  the  volatile 
products  from  the  coal.  Part  of  the  supply  comes  from 
the  gas  factories  as  a  by-product,  but  where  the  local 
supply  is  insufficient,  it  is  prepared  specially  for  smelters 
in  large  brick  ovens.  See  the  figure  below. 


FIG.  37.  —Coke  Oven. 
aa,  openings  for  slight  draught  at  first.    DD,  doors  for  removing  coke. 

The  coal,  in  car  loads,  is  shoveled  in  from  above ;  it  is 
then  ignited,  and  the  openings  on  the  side  almost  entirely 
closed.  In  the  course  of  several  hours  the  combustion  of 
the  lower  layer  of  coal  has  converted  the  remainder  into 
coke,  the  doors  are  opened,  and  the  coke  drawn  out. 

13.  Gas  Carbon.  — Gas  carbon  is  another  by-product  of 
coal-gas  manufacture.  Just  as  soot  collects  in  stove-pipes 
and  flues,  so  on  the  inside  of  the  retorts  there  is  gradually 
deposited  a  very  hard,  black  substance,  known  as  gas 
carbon.  This  is  occasionally  removed,  ground  up  fine, 


CARBON  AND  A  FEW  COMPOUNDS  139 

and  moulded  into  the  familiar  carbon  rods  in  our  electric 
arc  lights,  and  into  plates  for  electric  batteries. 

14.  Lampblack.  —  Lampblack  is  the  result  of  the  imper- 
fect combustion  of  any  substance  rich  in  carbon.     It  is 
usually  prepared  by  burning  some  hydrocarbon,  such  as 
turpentine,  C10H16,  in  a  limited  supply  of  air.     The  dense 
black  smoke  resulting  is  allowed  to  deposit  upon  canvas 
in  a  cool  room,  from  which  it  is  shaken,  and  is  then  ready 
for  commerce.     It  is  used  in  making  black  paint,  printers' 
ink,  etc. 

SOME  USES  OF  CARBON 

15.  As  a  Reducing  Agent.  —  In  the  form  of  charcoal  or 
coke,  at  a  high  temperature,  carbon  is  a  great  reducing  or 
deoxidizing  agent.     By  this  we  mean  that  when  it  is  heated 
with  the  oxides  of  various  metals,  it   has   the  power  of 
combining  with  the  oxygen  and  reducing  the  oxide  to  the 
metallic  condition.     This  will  be  made  clear  by  the  fol- 
lowing experiment. 

EXPERIMENT  86.  —  Make  a  small  cavity  near  one  end  of  a  stick  of 
charcoal,  and  put  therein  a  little  litharge,  PbO,  or  red  lead,  Pb3O4, 
and  heat  strongly  with  the  reducing  flame.  Notice  that  in  a  few 
minutes  a  bead  of  lead  appears  instead  of  the  oxide  that  we  had. 
The  carbon  has  combined  with  the  oxygen  in  the  lead  oxide  to  form 
carbon  djioxide,  and  the  lead  has  been  reduced  to  the  metallic  form. 

16.  As  an  Absorbent.  —  Carbon  in  the  form  of  charcoal 
is  an  excellent  absorbent,  not  only  of  gases,  but  of  certain 
other  substances  as  well. 

EXPERIMENT  87.  —  Thrust  a  piece  of  charcoal  under  water  and 
hold  it  there  a  minute  or  so.  What  is  seen  escaping  from  the  char- 
coal? Heat  another  piece  red-hot  and  plunge  under  water.  Are  the 
results  different?  Why?* 

*  In  this  connection  refer  to  Exp.  47,  under  ammonia. 


140  MODERN  CHEMISTRY 

EXPERIMENT  88.  —  Soak  some  vegetable  matter  in  a  vessel  of 
water  until  it  has  become  very  offensive,  on  account  of  decomposi- 
tion. Put  a  little  of  this  water  into  a  flask  and  add  some  bone-black 
or  powdered  charcoal,  and  shake  well.  Notice  that  the  disagreeable 
odor  disappears. 

17.  As  a  Purifier.  —  Application  is  made  of  this  fact  in 
purifying  cisterns  which  have  become  foul  with  decom- 
posing organic  matter.     The  charcoal  should  be  removed 
after  a  time  and  heated  to  redness  to  destroy  thoroughly 
the  organic  matter  which  may  have  been  absorbed.     It  is 
believed  that   partial    oxidation   takes   place  within   the 
pores,  but  unless  the  charcoal  is  heated  they  eventually 
become  clogged. 

EXPERIMENT  89.  —  Fit  a  filter  paper  smoothly  to  a  funnel  as 
described  in  Appendix  C,  page  365,  and  partly  fill  it  with  bone-black. 
Now  pour  upon  it,  slowly  at  first,  a  few  cubic  centimeters  of  logwood 
or  some  other  colored  vegetable  solution.  How  is  it  affected?  Try 
also  in  the  same  way  a  solution  of  copper  nitrate.  Are  the  results  the 
same? 

18.  .In  Refining.  —  An  application  of  the  power  of  char- 
coal to  absorb  vegetable  colors  is  made  in  refining  sugars. 
At  first  they  are  brown,  not  very  different  from  maple 
sugar  in  appearance.     This  raw  sugar,  as  it  is  called,  is 
dissolved  in  water  an/i  passed  through  filters  of  bone- 
black  which  absorb   the   coloring  matter  and  leave  the 
solution  clear.     This  may  be  shown  by  filtering  a  solu- 
tion of  molasses  in  water. 

EXPERIMENT  90.  —  In  like  manner,  charcoal  has  the  power  of  ab- 
sorbing various  organic  flavors.  Pass  through  a  powdered  char- 
coal filter  an  infusion  of  tea  or  coffee,  and  taste  it  after  it  has 
gone  through.  How  is  it  changed? 

19.  It  would  be  impossible  to  enumerate  the  various 
uses  of  carbon  in  its  different  forms.     Many  of  these  are 


CARBON  AND  A  FEW  COMPOUNDS  141 

familiar  to  the  student,  and  others  will  be  learned  from 
time  to  time.  Many  of  them  have  already  been  named  in 
the  sections  immediately  preceding  this. 

COMPOUNDS  OF  CARBOX.     THE  OXIDES 

20.  Carbon  Monoxide,  CO.  —  This  is  a  gas  obtained  when 
carbon  is  burned  in  a  limited  supply  of  air.     It  may  be 
prepared  by  passing  steam  over  red-hot  coke  or  charcoal, 
whereby  the  steam  is  decomposed,  thus:  — 

H20  +  C  =  CO  +  H2. 

It  is  also  produced  in  grates  and  base-burners.  At  the 
lower  portions  of  the  fire  where  the  heat  is  most  intense 
the  carbon  is  completely  burned,  producing  carbon  dioxide; 
as  this  passes  up  through  the  red-hot  coal,  it  unites  with 
another  portion  of  carbon  and  forms  the  monoxide. 
Again,  on  reaching  the  upper  surface,  the  monoxide  unites 
with  the  oxygen  of  the  air  and  is  burned  into  carbon 
dioxide. 

21.  Carbon  monoxide  may  be  prepared  in  an  impure 
form  by  heating  oxalic  acid  or  potassium  ferrocyanide  with 
sulphuric  acid,  or  by  passing  a  current  of  carbon  dioxide 
slowly  through  a  tube  containing  red-hot  charcoal  or  coke. 

22.  Characteristics  of  Carbon  Monoxide.  —  Carbon  mo- 
noxide is  a  colorless  gas,  having  a  faint,  peculiar,  but  some- 
what unpleasant  and  stifling  odor;    it  is  a  little  lighter 
than  air  and  burns  with  a  pale  blue  flame.     It  is  not 
soluble  in  water,  is  only  slightly  explosive  when  mixed 
with  air  or  oxygen,  and  is  poisonous  when  inhaled.     It 
has  the  power  of  decomposing  the  blood,  and  thus  of  ren- 
dering it  incapable  of  carrying  oxygen  and  removing  the 
waste  of  the  body.     On  this  account  serious  results  some- 
times follow  its  escape  into  rooms  from  coal  stoves  when 


142  MODERN  CHEMISTRY 

the  drafts  are  closed  at  night.  Open  charcoal  fires  also 
produce  the  same  gas,  and  have  sometimes  been  the  means 
of  causing  death. 

23.  As  a  Reducing  Agent.  —  It  has  been  seen  that  carbon 
is  a  strong  reducing  agent.  Carbon  monoxide  has  the 
same  properties,  owing  to  the  fact  that  it  has  strong 
affinity  for  more  oxygen,  to  form  carbon  dioxide.  The 
reduction  of  metallic  ores  in  blast  furnaces  is,  to  a  con- 
siderable extent,  due  to  this  property  of  carbon  monoxide. 
It  may  be  seen  by  passing  a  current  of  carbon  monoxide 
over  lead  oxide,  PbO,  heated  red  hot  in  a  tube.  The 
monoxide  abstracts  the  oxygen  from  the  lead  oxide,  form- 
ing carbon  dioxide  and  metallic  lead.  The  reaction  is  as 
follows:  -  pbQ  +  CQ  =  pb 


24.  Carbon  Dioxide,  C02.  —  Where  found.  —  This  gas  is 
always  found  in  the  air,  being  produced  by  the  combustion 
of  organic  bodies  and   by  respiration.     The   proportion 
varies  somewhat,  but  seldom  exceeds  four  parts  in  10,000 
parts  of  air.     Another  source  of  this  gas  as  found  in  the 
atmosphere  is  fermentation  and  decay. 

25.  Produced  in  Decomposition.  —  As  already  mentioned 
in  considering  ammonia,  organic  substances  are  very  un- 
stable and  readily  break  up  to  form  simpler  compounds. 
The  molecules  of  most  so-called  organic  compounds  consist 
of  carbon,  hydrogen,  oxygen,  and  often  nitrogen,  and  are 
usually  very  complicated.     In  the  processes  of  decay  the 
atoms  rearrange  themselves,  and  carbon  dioxide  is  one  of 
the  new  products.     The  process  is  the  same  when  fer- 
mentation is  induced  by  bacteria  or  germs,  such  as  those 
of  ordinary  yeast.     If  into  a  flask  containing  some  water 
sweetened  with  sugar  or  molasses  a  little  yeast  be  intro- 
duced, fermentation  very  soon  begins,  and  the  bubbles  of 


CARBON  AND  A  FEW  COMPOUNDS  143 

ga3  which  pass  off  may  be  collected  and  proved  to  be 
carbon  dioxide. 

26.  How  prepared.  —  For  laboratory  purposes  carbon 
dioxide  is  usually  prepared  by  treating  some  carbonate,  as 
marble,  CaCO3,  with  dilute  acid. 

EXPERIMENT  91.  —  Put  into  a  small  flask  some  marble,  coarsely 
powdered,  and  add  some  dilute  hydrochloric  or  nitric  acid.  Notice 
the  rapid  effervescence  and  evolution  of  colorless  gas. 

EXPERIMENT  92.  —  Collect  by  downward  displacement  a  bottle  of 
the  gas,  generated  as  above.  Lower  into  it  a  burning  match  or  candle  ; 
what  are  the  results  ?  Ignite  a  piece  of  magnesium  ribbon  and  hold 
it  in  a  bottle  of  carbon  dioxide;  what  are  the  results?  What  two 
products  are  formed?  Why  does  the  ribbon  continue  to  burn? 
Mention  some  other  gas  that  supports  the  combustion  of  phosphorus, 
but  not  that  of  ordinary  substances. 

EXPERIMENT  93.  —  To  show  the  density  of  the  gas.  Put  into  a  good- 
sized  bottle  or  beaker  a  small  candle  and  pour  in  upon  it  another 
bottle  of  carbon  dioxide.  You  cannot 
see  anything  being  turned  out,  but  the 
results  are  apparent.  This  is  sometimes 
made  more  effective  by  fastening  at 
short  intervals  upon  the  bottom  of  a 
trough  several  candles.  Lift  one  end  of 
the  trough  and  pour  down  it  a  large 
bottle  of  carbon  dioxide.  The  candles 
will  be  extinguished,  one  after  another, 
as  the  gas  reaches  them. 

EXPERIMENT  94.  —  Purpose  same  as 
preceding.  Put  into  an  evaporating  dish 
a  little  gasoline  and  ignite  it.  Take  a  large  bottle  of  carbon  dioxide 
and  pour  suddenly  upon  the  burning  oil.  The  flame  will  be  instantly 
extinguished. 

EXPERIMENT  95. —  To  show  effect  of  carbon  dioxide  on  limestone. 
Pass  a  current  of  carbon  dioxide  through  a  few  cubic  centimeters  of 
lime  water.  Notice  the  formation  of  a  white  precipitate,  which  is 
calcium  carbonate,  CaCO3,  of  the  same  composition  as  limestone. 
Continue  passing  the  gas  through  the  milky  solution ;  what  change 
takes  place  ?  Can  you  explain  ? 


144  MODERN  CHEMISTRY 

27.  Characteristics  of  Carbon  Dioxide.  —  From  the  above 
experiments  we  learn  that  carbon  dioxide  is  a  colorless^ 
odorless  gas,  considerably  heavier  than  air.     It  is  non- 
combustible  and  a  non-supporter  of  ordinary  combustion^ 
though  'such  substances  as  magnesium,  which  burns  with 
great  intensity,  are  able  to  decompose  the  gas  and  make 
use  of  the  oxygen.     It  is  slightly  soluble  in  water  and 
gives  to  the  latter  a  faint  acid  taste  and  reaction.     The 
presence  of  carbon  dioxide  may  always  be  determined  by 
its  effect  upon  lime-water.     It  forms  in  the  water  a  white 
precipitate  which  dissolves  slowly  again  in  excess  of  the 
dioxide.     Limestone  caves  are  a  manifestation  on  a  large 
scale  of  the  principle  shown  in   the  simple  experiment 
above.     Water  under  pressure  absorbs  considerable  quan- 
tities of   carbon  dioxide,  which  gradually  dissolves  the 
limestone  and  forms  caverns. 

28.  Liquid  Carbon   Dioxide.  —  Carbon  dioxide  may  be 
liquefied  in  strong  cylinders  by  pressure ;  if  the  pressure 
is  suddenly  withdrawn,  a  portion  of  the  liquid  is  rapidly 
vaporized,  producing  such  cold  as  to  convert  the  remainder 
into  a  white  crystalline  solid  like  snow.    The  temperature  of 
this  carbonic  acid  snow  is  sufficiently  low  to  freeze  mercury. 
The  solid  carbon  dioxide  vaporizes  without  first  melting. 

29.  Choke  Damp.  —  Because  of  its  density,  carbon  di- 
oxide frequently  collects  in  deserted  mines  and  deep  wells, 
and  is  called  by  miners  "choke  damp."     Its  presence  in 
such  places,  however,  may  always  be  detected  by  lowering 
to  the  bottom  a  burning   candle   or   lantern.     Carbonic 
anhydride  is  another  name  for  the  same  gas,  it  being  the 
anhydride  of  the  unstable  acid,  H2CO3.     It  is  still  popu- 
larly called  carbonic  acid  gas. 

30.  Uses  of  Carbon  Dioxide.  —  Carbon  dioxide  is  used 
extensively  in  making  "soda  water."     It  is  confined  in 


CARSON  AND  A  FEW  COMPOUNDS  145 

strong  cylinders  under  great  pressure,  and  allowed  to 
flow  into  cold  water  in  strong  tanks  also  under  pressure. 
The  water  is  thus  thoroughly  charged.  When  the  stop- 
cock is  turned  and  the  water  flows  into  the  glass,  the 
pressure  being  removed,  the  carbon  dioxide  rapidly  bubbles 
out.  It  is  this  gas  which  gives  the  sharp  biting  taste  to 
soda  water  and  also  to  the  water  of  many  mineral  springs. 
It  is  the  same  gas  that  causes  the  effervescence  in  beer  and 
the  sparkling  appearance  of  some  wines. 

31.  In  some  of  our  cities  carbon  dioxide  is  now  being  put 
upon  the  market  in  small  oval-shaped  steel  vessels  into  which 
the  gas  is  forced  under  great  pressure.     When  ready  for 
use,  a  valve  is  opened,  the  gas  rushes  into  a  glass  of  water 
flavored  and  sweetened,  and   the   soda  water  is  ready. 
These  sparklets,  as  the  steel  vessels  are  called,  are  very 
small,  and  a  large  number  may  be  carried  without  great 
inconvenience.      In    Germany   the    same   article   is   sold 
under   the   name   of   Sodors.     Certain  fire  extinguishers 
owe  their  value  to  the  large  quantities  of  carbon  dioxide 
contained ;  and  instances  are  on  record  in  which  fires  in 
coal  mines  which  have  defied  all  other  means  have  been 
extinguished  by  passing  in  carbon  dioxide. 

32.  Though  this  gas  cannot  be  inhaled  in  any  consider- 
able quantities,  it  is  not  poisonous,  but  like  water  causes 
death  by  shutting  out  the  oxygen.     Hence  a  person  might 
drown  in  a  well  or  vat  of  carbon  dioxide  just  as  readily  as 
in  one  of  water.     To  plant  life,  however,  the  gas  is  in- 
dispensable ;    it   is   inhaled   by  plants   as   oxygen   is   by 
animals,  and  in  the  presence  of  light  the  life  forces  of  the 
plant  are  sufficient  to  decompose  the  compound  into  its 
constituents.     The   carbon   is  stored   up   in   the   woody 
structure  of  the  tree  or  plant,  and  the  oxygen  is  given  off 
again   to  the   air.     Thus   a  considerable  portion  of   the 


146  MODERN   CHEMISTRY 

carbon  in  all  our  forests  and  coal  beds  was  once  in  the 
form  of  gaseous  carbon  dioxide  in  the  atmosphere. 

THE  HYDROCARBONS 

33.  Definition.  —  By   this   term   we    mean   those   com- 
pounds consisting  of  carbon  and  hydrogen,  of  which  there 
are  many.     The  most   important  are   the   three   follow- 
ing:— 

Marsh  Gas     ....     CH4 

Olefiant  Gas  ....     C2H4 

Acetylene       .     .     .     .     C2H2 

34.  Marsh  Gas.  —  This  is  also  known  as  methane,  and 
by  miners  asfire  damp.     It  is  often  found  in  coal  mines  as 
the  result  of  the  decomposition  of  organic  matter,  and  in 
swamps  from  the  same  source.     By  stirring  the  leaves  and 
similar  matter  that  collect  upon  the   bottoms  of  ponds, 
bubbles  of  gas,  consisting  largely  of  marsh  gas,  are  seen 
to  rise.      It  is  always  produced  in  the  destructive  dis- 
tillation of  any  organic  matter,  such  as  the  preparation  of 
charcoal  in  retorts  or  that  of  illuminating  gas  from  coal. 

35.  Characteristics  of  Marsh  Gas.  —  Marsh  gas  is  a  color- 
less,  odorless  gas,  the  lightest  of  all  except   hydrogen, 
having  a  specific  gravity  compared  with  air  of  less  than 
0.6.     It  is  highly  inflammable,  burning  with  a  pale  blue 
flame,  and  with  air  or  oxygen  forms  a  dangerous  explosive 
mixture.     It  is  by  this  gas  that  most  explosions  in  coal 
mines  are  caused,  and  on  this  account  it  is  called  fire  damp, 
the  word  damp  with  miners  being  a  generic  term  meaning 
gas.     Marsh   gas  is  somewhat  soluble  in  water,  and   is 
neutral  to  test  paper,  affecting  neither  red  nor  blue.     It  is 
an  important  constituent  of  ordinary  coal  gas,  and  when 
burned  produces  much  heat. 


CARBON  AND  A  FEW  COMPOUNDS  147 

36.  Protection  against  Fire  Damp.  —  If  you  hold  a  wire 
screen  over  the  flame  of  a  Bunsen  burner,  you  will  see 
that  the  flame  does  not  pass  through  it,  although  if  you 
bring  a  lighted  match  above  the  screen,  you  will  find 
there  a  combustible  gas.     This  is  because  the  wire  cloth, 
being  a  good  conductor  of  heat,  withdraws  it  from  the 
burning  gas  and   so   lowers  the  temperature  that  what 
has  passed  through  no  longer  burns.    Now  hold  the  screen 
in  the  flame  until  it  becomes  red  hot ;  the  gas  above  will 
be  ignited  and  continue  to  burn. 

An  observation  of  these  facts  led  Sir  Humphry  Davy 
to  design  the  "  safety  lamp  "  which  now  bears  his  name. 
It  is  little  more  than  an  ordinary  miner's  lamp  sur- 
rounded by  a  wire  screen.  If  the  miner  enters  a  chamber 
filled  with  fire  damp,  though  the  gas  may  burn  on  the 
inside  of  the  screen,  there  is  no  danger  unless  he  remains 
until  the  wire  becomes  hot  enough  to  ignite  the  gas 
outside. 

37.  Olefiant  Gas,  C2H4.  —  This  also  is  a  constituent  of 
common  illuminating  gas,  and  is  formed  in  the  destructive 
distillation  of  wood  and  coal.      It  may  be  prepared  by 
heating  ethyl  alcohol  with  sulphuric  acid.     Really,  two 
reactions  take  place  ;  first  an  ethyl  ester  of  sulphuric  acid 
is  formed,  C2H5HSO4,  which  very  soon  breaks  down  into 
ethylene  and  sulphuric  acid.     The  final  result  is 

C2H5OH  +  H2S04  =  C2H4  +  H2S04,  H2O. 

38.  Characteristics  of  Olefiant  Gas. — Ethylene,  as  this 
gas  is  also  called,  is  of  about  the  same  density  as  air,  is 
colorless,  has  a  faint  odor,  and  burns  with  a  yellowish 
white  light,  such  as  is  seen  in  the  ordinary  gas  jet.     It 
is  somewhat  explosive  when  mixed  with  air  or  oxygen ; 
at  40  atmospheres'  pressure  it  is  reduced  to  a  liquid. 


148  MODERN  CHEMISTRY 

ACETYLENE,  C2H2 

39.  How  prepared.  —  This  gas  is  formed  in  small  quao* 
tities  together  with  other  hydrocarbons  in  the  distillation 
of  wood  and  coal.     It  is  prepared  now  in  large  quantities 
by  treating  calcium  carbide,  CaC2,  with  water,  as  follows  :  — 

CaC2  +  H20  =  CaO  +  C2H2.   ' 

The  lime,  CaO,  thus  formed  immediately  reacts  with  an- 
other molecule  of  water,  forming  slaked  lime,  or  calcium 
hydroxide,  Ca(OH)2,  thus  :  — 

CaO  +  H2O  =  Ca(OH)2. 

The  final  reaction  then  would  be  indicated  by  — 
CaC2  +  2  H2O  =  C2H2  +  Ca(OH)2. 

40.  Calcium  Carbide.  —  Calcium  carbide  is  a  dark  gray 
solid,  more  or  less  crystalline  in  appearance,  always  giving 
off  the  odor  of  acetylene,  owing  to  its  decomposition  by 
the  moisture  in  the  air.     In  America  the  greater  portion 
of  the  commercial  supply  comes  from  Niagara  Falls,  where 
it  is  prepared  by  fusing  at  intense  heat  in  electrical  fur- 
naces  pure  lime  intimately  mixed  with  charcoal   finely 
pulverized.     When  taken  from  the  furnace,  it  is  packed 
in  metallic  drums,  sealed  air-tight,  and  is  then  ready  for 
shipment. 

EXPERIMENT  96,  —  Into  a  test-tube  put  a  small  lump  of  calcium 
carbide,  cover  with  water,  and  quickly  insert  a  cork  with  delivery  tube 
and  jet  attached.  Notice  the  violent  chemical  action  and  the  odor  of 
the  gas.  Light  the  jet  and  notice  with  what  kind  of  a  flame  it  burns. 

41.  Another  Method.  —  Sometimes  this  method  is  varied 
slightly  by  using  a  flask   fitted   with   a   two-hole   cork. 
Through  one  hole  passes  the  delivery  tube,  through  the 


CARBON  AND  A  FEW  COMPOUNDS 


149 


other  a  funnel  with  a  stop-cock.  In  this  way  the  flow  of 
water  can  be  regulated  and  the  rapid  evolution  of  gas 
prevented.  Precaution  must  be  taken  in  this  case  not  to 
light  the  jet  too  soon,  as  acetylene  mixed  with  air  is  dan- 
gerously explosive. 

42.  Acetylene  Generators.  —  This  illustrates  one  class 
of  acetylene  generators  now  offered  upon  the  market,  in 
which  the  water  is  allowed  to  drip  on  the  carbide.  The 
objection  to  this  is  that  with  the  small  supply  of  water 
the  carbide  becomes  so  warm  as  to  bring  about  a  partial 
decomposition  of  the  acetylene  into  other  undesirable 
hydrocarbons. 

EXPERIMENT  97.  —  For  class-room  work  an  excellent  generator 
may  be  prepared  thus :  procure  a  tin  can,  holding  a  quart  or  two, 
and  having  a  screw  top.  (A  can  in  which  some 
varieties  of  coffee  are  sold  will  do.)  To  the 
inside  of  the  screw  top  solder  a  hook.  Upon  this 
suspend  a  small  bucket  or  basket  made  from  a 
tin  can,  and  having  a  wire-cloth  or  perforated 
bottom.  Cut  out  the  bottom  of  the  larger  can  as 
shown  in  the  cross-sectional  view  6  of  the  accom- 
panying figure ;  then  solder  two  strong  bent 
wires,  W,  W,  upon  opposite  sides  of  it. 

Xow  obtain  another  can  just  large  enough  to 
allow  the  first  to  move  up  and  down  easily  within 
it.  Melt  or  cut  out  the  top ;  then  cut  down  two 
flaps  about  three-fourths  of  an  inch  deep,  and 
bend  them  to  a  horizontal  position,  as  at  F. 
Through  each  flap  punch  a  hole  large  enough  to 
receive  the  bent  guide-wires  soldered  on  to  the 
other  can.  Near  the  bottom  cut  a  round  hole 
and  insert  a  rubber  cork,  through  which  passes 
a  bent  delivery  tube  extending  up  nearly  to  the 
top  of  the  can. 

When  ready  for  work  fill  this  can  nearly  full 
of  water,  put  some  carbide  into  the  basket,  sus- 
pend it  upon  the  hook  and  then  lower  the  first  FIG.  39. 


150  MODERN  CHEMI8TEY 

can  into  position,  the  guide-wires  passing  through  the  openings  in  the 
flaps.  The  screw  top  enables  one  to  refill  the  basket  without  remov- 
ing the  entire  cylinder.  As  soon  as  the  carbide  touches  the  water, 
acetylene  will  begin  to  form,  and,  mixed  with  air,  will  flow  from  the 
delivery  tube  T. 

This  generator,  which  illustrates  another  class  now  upon  the  mar- 
ket, is  automatic.  In  case  the  delivery  tube  becomes  clogged,  the 
increasing  pressure  of  the  gas  will  lift  the  inner  cylinder,  and  with  it 
the  basket  of  carbide,  from  the  water.  Or,  if  the  guide-wires  become 
caught  and  prevent  this,  the  pressure  on  the  water  will  cause  it  to 
flow  out  over  the  flaps.  In  either  case  the  rapid  evolution  of  gas  will 
soon  cease. 

CAUTION.  —  Before  beginning  the  generation  of  acetylene 
be  sure  no  lights  are  in  close  proximity,  and  allow  the  first 
gas  generated  to  escape.  It  contains  too  much  air  for 
good  results  and  is  too  dangerous.  With  these  precau- 
tions the  gas  may  be  used  direct  from  the  generator,  or 
first  passed  into  an  ordinary  gasometer,  which 
any  tinner  can  make  cheaply. 

43.  Acetylene  Burners.  —  But  to  secure  steadi- 
ness of  flow  and  safety,  it  is  always  better  to 
pass  the  gas  through  an  acetylene  burner  or 
tip,  which  differs  from  the  tip  of  an  ordinary 
gas  jet  only  in  that  instead  of  a  slit  there  are 
two  very  small  openings  drilled,  oblique  to  each 
other.  See  Fig.  40  ;  a  is  a  cross-sectional  and 
b  the  top  view.  These  tips  are. very  cheap, 

and  safe  because  the  openings  for  the  exit  of 
FIG.  40. 

gas  are  so  small  that   the    flame   cannot  pass 

back  into  the  generator ;  c  shows  another  form  of  tip 
frequently  used.  The  two  openings  compel  the  issuing 
jets  of  gas  to  strike  each  other  obliquely,  as  in  a. 

44.  Characteristics  of  Acetylene.  —  Acetylene  is  a  color- 
less gas,  of  an  ethereal  odor  when  perfectly  pure,  but  as 


CARBON  AND  A  FEW  COMPOUNDS  151 

ordinarly  obtained  it  is  very  offensive  to  the  smell.  It 
is  soluble,  volume  for  volume,  in  water  and  very  explo- 
sive when  mixed  with  oxygen  or  air.  An  ordinary  jet 
of  acetylene  burns  with  a  yellowish  flame,  and  owing  to 
the  large  proportion  of  carbon,  —  over  92  per  cent,  —  it 
gives  off  considerable  soot.  With  a  burner  like  the  one 
described  above  it  furnishes  an  intensely  white  light,  rival- 
ing the  calcium  or  Drummond  light  in  brilliancy ;  so  that 
it  is  now  frequently  used  for  projecting  lantern  slides 
upon  screens  and  for  bicycle  lamps. 

45.  Intense  Heat.  —  Fine  iron  wires  held  in  the  flame 
are  quickly  consumed,  throwing  off  sparks  as  if  burning 
in  oxygen. 

When  used  in  a  blast  lamp  instead  of  common  gas,  acety- 
lene burns  with  a  bluish-white  flame.  The  intensity  of 
this  is  sufficient  to  melt  copper  wires  readily,  and  ordinary 
platinum  wires  in  two  or  three  minutes ;  furthermore,  it 
will  even  soften  porcelain.  Iron  wires  a  sixteenth  of  an 
inch  in  diameter  are  quickly  fused  and  burn  with  a  most 
brilliant  shower  of  sparks,  especially  when  a  molten 
globule  of  iron  upon  the  end  of  the  wire  is  suddenly  oxi- 
dized, and  being  thrown  out  into  the  air  breaks  into  a 
shower  of  stars.  Watch-springs  and  knife-blades  may  be 
as  easily  burned  away.  In  a  darkened  room  the  display 
is  very  beautiful. 

46.  Blowpipe  for  Experiments. 
—  The    blowpipe    best    suited   to 
this  work  may  be  made  by  almost 
any  student.     See  Fig.  41.     The 
outer  part,  B,  is  the  ordinary  black 
japanned   blowpipe,  costing   only 
a    few    cents.       A    hole    is    cut 

through   at  the   point  E,  for  the  insertion  of  an  inner 


152  MODEEN  CUEMISTRY 

tube,  which  may  be  made  by  carefully  straightening  an 
ordinary  eight-inch  brass  blowpipe.  Solder  this  firmly 
in  place,  plug  the  mouth  end  of  the  outer  pipe  with  a  piece 
of  brass  through  which  a  small  hole  has  been  drilled,  and 
the  acetylene  blowpipe  is  complete.  Connect  the  inner 
tube  with  the  foot-bellows  furnishing  the  air,  and  the 
outer  tube  with  the  acetylene  tank,  through  the  acetylene 
tip.  Regulate  by  means  of  a  stop-cock  the  flow  of  gas, 
so  that  when  in  operation  the  acetylene  is  completely 
burned,  with  the  flame  almost  entirely  blue. 

47.  From  these  experiments  it  will  be  seen  that  the  heat 
of  this  flame  is  intense,  reaching  probably  2000°  C. 

EXPERIMENT  98.  —  To  show  the  explosiveness  of  acetylene.  In  the 
center  of  the  bottom  of  a  pound  baking-powder  can  punch  a  small 
hole.  Place  the  can,  bottom  upward,  for  a  minute  or  so  over  a  tube 
delivering  acetylene,  then  set  upon  the  table  in  the  same  position. 
Bring  a  flame  to  the  touch-hole,  when,  if  the  proportions  are  suitable, 
a  violent  explosion  will  ensue,  and  the  can  will  be  thrown  several  feet 
into  the  air.  If  too  much  acetylene  has  been  introduced,  it  may  burn 
quietly  a  moment  at  the  opening,  until,  as  more  air  enters  at  the 
bottom  to  take  the  place  of  the  gas  burned,  an  explosive  mixture  is 
formed  and  a  report  follows. 

ILLUMINATING  GASES 

48.  One  of  the  most  important  of  these  has  just  been 
considered.    It  is  new  as  an  illuminant,  and  some  problems 
in  connection  with  it  have  not  been  entirely  solved,  but  it 
is  already  being  extensively  applied  in  many  of  the  smaller 
towns  where  no  gas  plant  exists,  for  railway  lighting,  bi- 
cycle lamps,  etc.     The  fact  that  thus  far  no  appliance  has 
been  invented  for  using  it  in  cooking,  for  the  reason  that 
the  excess  of  carbon  covers  the  utensils  with  a  deposit  of 
soot,  has  prevented  a  much  more  extensive  use. 


CAEBON  AND  A  FEW  COMPOUNDS 


153 


OTHER  ILLUMINANTS 

49.  Besides  acetylene,  ordinary  or  coal  gas,  "water" 
gas,  and  Pintsch  gas  deserve  notice. 

50.  Coal    Gas.  —  This   is  obtained  by  the  destructive 
distillation  of  coal  in  iron  retorts.     The  following  diagram 
illustrates  the  essential  features  of  a  gas  plant. 


FIG.  42.    A  Gas  Plant. 

51.  Preparation.  —  Soft  coal  is  shoveled  into  the  retort, 
beneath  which  is  the  furnace,  F.      When  the  retort  is 
filled,  the  door  is   luted  on  air-tight.      The   heat  from 
the  furnace  drives  out  the  gaseous  products   from   the 
coal  in  the  retorts,  and  they  are  carried  up  to  the  hy- 
draulic main,  H.     From  here  the  gas  is  forced  by  means 
of  pumps,  not  shown  in  the  diagram,  through  the  con- 
densers, a  series  of  pipes  several  hundred  feet  in  length, 
where  it  is  cooled  and  the  tar  condensed.     This  by-product 
is  drawn  off  by  pipes,  P,  to  the  tar- well,  T,  from  which  it 
is  pumped  into  barrels. 

52.  From  the  condensers   the   gas   goes   through   the 
scrubber,  a   large   cylindrical   tank   filled   with   coke   or 
lattice  work,   over   which  water  slowly  trickles.      The 


154  MODERN  CHEMISTRY 

partition  through  the  center  causes  the  gas  to  flow  down 
one  side  and  up  the  other;  the  coke 'breaks  up  the  gas 
into  bubbles,  so  as  to  secure  a  thorough  washing.  Here 
the  ammonia  is  mostly  removed,  and  the  impure  aqua 
ammonia  thus  obtained  is  drawn  off  at  intervals,  neutral- 
ized with  acids,  and  treated  with  lime  for  the  preparation 
of  the  ammonia  of  commerce,  as  already  described. 

53.  The  gas  next  passes  through  the  lime  purifiers,  a 
number  of  low  cylindrical  tanks,  containing  lime  spread 
upon  horizontal  shelves.     The  lime  dries  the  gas  and  at 
the   same    time    removes   the  sulphureted  hydrogen  and 
the  carbon  dioxide.     In  some  works,  ferric  oxide,  Fe2O3, 
is  used  for  the  same  purpose.     From  the  purifier  the  gas 
passes  to  the  gas-holder,  a  very  large  tank,  where  it  is 
stored  for  use. 

On  the  inside  of  the  retorts,  as  previously  stated,  there 
gradually  collects  a  fine,  hard  deposit,  known  as  gas  car- 
bon, which  is  now  a  very  useful  by-product. 

54.  Water  Gas.  —  This  gas  receives  its  name  from  the 
fact  that  steam  is  used  in  one  part  of  the  process  of  manu- 
facture.    From  the  boilers  steam  is  passed  into  chambers, 
or   pipes,   containing  charcoal  or  coke,   heated  red  hot. 
Here  the  vapor  and  coke  react  upon  each  other,  the  former 
being  decomposed,  thus  :  — 

C  +  H20  =  CO  +  H2. 

Two  gases,  carbon  monoxide  and  hydrogen,  mixed  to- 
gether, are  thus  obtained.  Both  are  combustible,  and  in 
burning  produce  great  heat,  but  neither  gives  any  light. 
This  mixture,  therefore,  is  next  allowed  to  pass  into  re- 
torts, kept  at  a  high  temperature,  into  which  kerosene,  or 
some  similar  oil,  is  sprayed.  The  heat  vaporizes  and  de- 
composes the  oil  into  hydrocarbons  that  do  not  liquefy 


CARBON  AND  A  FEW  COMPOUNDS  155 

again  upon  cooling,  and  which  burn  with  a  luminous 
flame.  This  last  step  is  called  "carbureting,"  and  by 
it  a  gas  is  obtained  not  very  different  in  composition  from 
coal  gas. 

55.  Pintsch  Gas.  — This  is  the  gas  so  frequently  used 
for  lighting  street  cars  and  railway  coaches.     It  received 
its  name  from  its  inventor,  who  sought  to  improve  the  old 
and -very  unsatisfactory  method  of  lighting  coaches  in 
England  by  means   of   candles.     The   essential   features 
of  manufacture   are   similar    to    those   of   the    coal    gas 
plant.      Naphtha   is   sprayed   into    retorts    heated   suffi- 
ciently to  decompose  the  vaporized  oil  into  other  hydro- 
carbons.    These   are   then  passed  through  an  improved 
form  of  condenser,  a  washer,  and  lime  purifiers  into  the 
gasometer. 

56.  Next  the  gas  is  drawn  through  a  cylinder  known  as 
the  "  freezer,"  or  "  dryer."     Here,  owing  to  the  action  of 
the  pumps,  it  expands,  and  being  cooled  thereby,  loses  all  its 
moisture.     The  same  pumps  force  the  gas  into  large  tanks 
called  "accumulators,"    from  which  it  is  drawn  off  into 
smaller  tanks  for  shipment  from  place  to  place,  or  directly 
into  the  storage  cylinders,  so  frequently  seen  under  railway 
coaches.     This  light  possesses  not  only  the  advantages  of 
intensity  and   whiteness,  which   coal   gas,    as   ordinarily 
burned,  lacks,  but  unlike  ordinary  gas,  its  illuminating 
power  is  only  slightly  decreased  by  strong  pressure  such 
as  is  necessary  for  transportation  in  storage  cylinders. 

57.  Natural  Gas.  —  Natural  gas  is  formed  by  the  de- 
composition of  organic  matter,  and  the  main  constituents 
are  about  the  same  as  those  of  the  other  mixed  gases  used 
for  illumination. 

58.  Composition  of  Illuminating  Gases.  — With  the  ex- 
ception of  acetylene,  the  illuminating  gases  noticed  are  all 


156  MODERN  CHEMISTRY 

mixtures.     The  most  important  constituents  of  coal  and 
"  water  "  gas  are  given  below  :  — 

COAL  GAS 

Hydrogen       .     .     .     .  H,       about  46  per  cent. 

Marsh  Gas      ....  CH4        "      38 

Olefiant  Gas   ....  C2H4,      "        2 

Carbon  Monoxide     .     .  CO,         "      11 

Small  amounts  of  higher  hydrocarbons,  and  such  impuri- 
ties as  hydrogen  sulphide,  ammonia,  and  carbon  dioxide. 

WATER  GAS* 

Marsh  Gas CH4 

Carbon  Monoxide     .     .     .CO 
Hydrogen        H 

Small  amounts  of  higher  hydrocarbons. 

SUMMARY  OF  CHAPTER 

Classification  of  free  forms  of  carbon. 
Description,  preparation,  and  uses  of. 

a.  Diamonds. 

b.  Graphite. 

c.  Coals. 

Origin  of  natural  coal. 
Varieties  of  and  differences. 
Petroleum  and  products  from  it. 

d.  Charcoal. 

e.  Coke. 

/.  Gas  carbon. 
g.  Lampblack. 

*  Water  gas  contains  a  larger  proportion  of  carbon  monoxide  than 
ordinary  coal  gas;  otherwise  the  two  are  not  very  different. 


CARBON  AND  A  FEW  COMPOUNDS  157 

Reducing  power  of  carbon. 
Meaning  of  term. 
Experiment. 
Absorbing  power. 

For  various  substances. 
Practical  applications  of  this  power. 
Compounds  of  carbon. 

The  oxides  —  Names  and  formulae. 
Preparation  of  CO. 
Characteristics. 
Sources  of  CO2  in  the  air. 
Laboratory  method  of  preparing. 
•    Characteristics  of  CO2. 

Experiments  to  illustrate  same. 
•Practical  uses  of  CO2. 

Soda  water,  sparklets,  sodors,  etc. 
Hydrocarbons  —  Meaning  of  term. 

Three  important  hydrocarbons. 
Marsh  gas  —  Sources  of,  in  the  air. 
Characteristics. 
Protection  against  explosions. 
Olefiant  gas  —  Where  found. 
Characteristics  of. 
Compare  witli  marsh  gas. 
Value  of  each  in  coal  gas. 
Acetylene  —  How  prepared  for  use. 
Manufacture  of  carbide. 
Description  of  acetylene  generators. 
Description  of  acetylene  tips. 
Characteristics  of  acetylene. 
Experiments   to    show  its  lighting,  heating,   and 

explosive  properties. 
Other  illuminating  gases. 
Coal  gas. 

Method  of  preparing  —  Apparatus. 

Plans  for  purifying. 

Different  forms  of  gas-burners. 

Valuable  ^-products  —  How  secured  —  Use. 


158  MODEEN  CHEMISTRY 

Water  gas. 

How  prepared. 

Characteristics  of. 

Comparison  with  coal  gas  in  composition. 
Pintsch  gas. 

Method  of  preparing  and  purifying. 

Used  where. 

Comparison  with  coal  gas.    . 


CHAPTER  XII 

« 

FUNDAMENTAL  LAWS  OF  CHEMISTRY 

1.  Quantitative  Work.  —  It  may  have  *seemed  to  the 
student  that  the  quantity  of  a  reagent  used  in  any  experi- 
ment makes  little  difference.  While  definite  amounts  are 
usually  specified,  care  is  not  often  taken  to  use  exactly 
that  quantity.  Generally  the  result  will  be  the  same,  but 
if  more  than  the  necessary  amount  of  a  substance  is  used, 
the  excess  remains  and  is  simply  wasted.  This  fact  is 
usually  stated  in  what  is  known  as  — 

V  2.  The  Law  of  Definite  Proportions.  —  Briefly,  it  is  this: 
Two  or  more  elements,  in  uniting  to  form  a  compound,  always 
do  so  in  the  same  proportion  by  weight.  This  has  been 
illustrated  somewhat  in  the  earlier  part  of  the  book  in 
discussing  compound  bodies.  It  is  a  very  important  law, 
and  upon  it  much  of  the  science  of  chemistry  depends., 
To  illustrate  it  more  fully  the  student  should  make  Jjie 
following  experiments,  using  the  utmost  care  to  insure 
accuracy.  Let  him  not  draw  his  conclusions  beforehand 
and  then  endeavor  to  make  his  results  conform  to  these. 

EXPERIMENT  99. —  Fill  two  burettes,  one  with  a  solution  of  caustic 
soda  and  the  other  with  dilute  hydrochloric  acid,  and  support  them 
upon  a  stand.  Carefully  take  the  reading  of  each,  using  the  lowest 


HP        FUNDAMENTAL  LAWS  OF  CHEMISTRY  159 

part  of  the  meniscus  in  doing  this,  as  shown  in  the  figure.  Here 
the  lowest  part  of  the  curve  coincides  with  38.4,  and  this  would  be 
the  reading. 

Now  find  the  weight,  as  accurately  as  possible,  of  a  small 
evaporating  dish.  Much  time  can  be  saved  here  if  each 
student  will  provide  himself  with  a  small  pasteboard  box 
and  cover,  such  as  blank  labels  are  packed  in.  Put  the  box 
and  cover  upon  the  scale  pan  opposite  to  the  dish,  and  pour 
in  fine  shot  or  sand  until  it  is  exactly  counterpoised.  This 
Represents  the  -weight  of  the  dish.  Put  the  box  with  its 
contents  away  where  it  will  be  safe  from  accident. 

Now,  from  the  caustic  soda  burette  allow  10  cc.  to  flow 
into  the  evaporating  dish,  and  add  one  drop  of  phenolphthal- 
ein  solution,  or,,  if  more  convenient,  enough  litmus  solution 
to  give  a  decidecf  blue  color.  From  the  other  burette,  with 
constant  stirring,  let  the  acid  flow  in  slowly  until  the  color  given 
by  the  phthalein  barely  disappears,  or  until  the  blue  litmus  just  shows 
pink.  Take  the  reading  of  the  acid  burette,  and  by  subtracting 
the  previous  reading  determine  how  much  hydrochloric  has  been 
used.  The  change  in  the  color  noted  above  indicates  that  sufficient 
acid  has  been  added  to  neutralize  the  alkali  and  form  therewith 
.a  salt." 

Now  place  the  evaporating  dish  upon  a  ring-stand,  or  better  upon 
a  sand-bath,  and  evaporate  slowly  to  dryness.  Do  not  let  the  liquid 
boil,  as  some  will  be  lost  by  spurting  out,  and  be  careful  toward  the 
close  to  withdraw  the  heat  before  the  solution  is  entirely  dry,  lest  the 
dish  become  so  warm  as  to  decompose  some  of  the  salt.  If  the  heat 
*  of  the  dish  does  not  complete  the  evaporation,  warm  it  very  gently  for 
another  moment.  When  perfectly  dry  let  the  dish  cool,  and  weigh  it. 
In  doing  this  put  the  small  box  and  shot  upon  the  opposite  pan  as  be- 
*  fore,  then  whatever  weights  are  necessary  to  add  will  represent  the 
vwight  of  the  salt  obtained.  If  the  shot  are  not  used,  subtract  the  first 
weight  from  the  second.  Tabulate  results  as  below:  — 

Wt.  of  dish  +  salt  .  .  17.103  Caustic  soda  used  .  .  10:0  cc. 
Wt.  of  dish  ....  15.217  HC1  used 6.4  cc. 

Wt.  of  salt 1.886 

EXPERIMENT   100.  —  Purpos^   a  continuation  of  the  preceding. 
Repeat  the  preceding  experiment,  using  the  same  amount  of  caustic 


160  MODERN  CHEMISTRY 

soda,  but  twice  as  much  acid.     The  litmus  or  phthalein  need  not  be 
added.     Use  the  same  precautions  as  before.     Tabulate  results. 

Wt.  of  dish  +  salt     .     .      Caustic  soda  used     .     .     10.0  cc. 

Wt.  of  dish      ....     15.217         HC1  used 12.8  cc. 

Salt 

EXPERIMENT  101.  —  Purpose,  same  as  above.  Repeat,  using  5  cc. 
of  caustic  soda  solution,  a  few  drops  of  litmus  or  one  of  phthalein,  and 
then  enough  hydrochloric  to  neutralize,  as  in  Experiment  98.  Cool 
and  weigh  as  before. 

3.  Comparison  of  Results.  —  Comparing  the  results  ob- 
tained, we  may  formulate  them  as  below  :  —  • 

Exp.    99.    NaOH  used  .  .  10.0  cc.        Salt  (NaCl)  obtained  .  .    — 

HC1  «  .  .  6.4  cc. 

Exp.  100.  NaOH  used  .  .  10.0  cc.  NaCl  obtained — 

HC1  «  .  .  12.8  cc. 

Exp.  101.  NaOH  used  .  .  5.0  cc.  NaCl  obtained — 

HC1         «     .  . 

4.  What  evidence  in  the  above  experiments  do  you  find 
in  proof  of  the  law  of  definite  proportions  ?     Is  there  any 
agreement  between  the  first  and  second  of  the  above? 
Between  the  second  and  third  ?     Why  ? 

EXPERIMENT  102.  —  Further  proof  of  the  law.  Carefully  weigh  an 
evaporating  dish  or  find  its  equivalent  in  shot  as  before,  then  add  a  half- 
gram  weight  to  the  pan  on  which  the  shot  is,  and  put  into  the  evaporat- . 
ing  dish  sodium  carbonate  crystals  to  balance.  Add  a  few  centimeters 
of  pure  water  to  the  carbonate,  and  then  add  dilute  hydrochloric  acid,  a 
little  at  a  time.  Keep  the  dish  covered  with  a  sheet  of  glass  or  watch 
crystal  so  as  not  to  lose  any  by  its  spattering  out.  In  this  way  cap- 
tiously add  the  acid  until  the  carbonate  is  all  dissolved,  or  until  it  no 
longer  effervesces.  Now  rinse  off  the  cover-glass  into  the  evaporating 
dish,  and  evaporate  to  dryness  with  the  same  precautions  used  before. 
Cool,  weigh,  and  determine  the  amount  of  salt  obtained. 

Sod.  Carb. :  Na2CO3  +  dish      .     .      —        NaCl  +  dish      .    .       — 

Wt.  of  dish      .     .     .  Dish 

~*^       NaCl — 


FUNDAMENTAL  LAWS  OF  CHEMISTRY  161 

EXPERIMENT  103.  —  Same  as  preceding.     Pursue  the  same  method 
as  above,  using  1  g.  of  the  carbonate  instead  of  a  half  gram. 

Used :  Na2CO3  +  dish  .  .  Obtained :  NaCl  +  dish    .  . 

Wt.  of  dish  .  —  Dish  .  — 


Na2C03 —  NaCl — 

EXPERIMENT  104.  —  Purpose,  same  as  before.     Repeat  the  preced- 
ing, using  this  time  1£  g.  of  sodium  carbonate  crystals.     Results :  — 

Used:  Na2CO3  +  dish  .  .  Obtained :  NaCl  +  dish   .  . 

Dish  .  Dish  .  — 


1.500  NaCl 


5.  Summary.  —  In  each  of  the  last  three  experiments 
find  the  ratio  existing  between  the  carbonate  used  and  the 
salt  obtained. 

1.  Na2CO3  :  NaCl  :  :  1  :  x  = 

2.  Na2C03  :  NaCl  :  :  1  :  y  = 

3.  Na2C03  :  NaCi  :  :  1  :  z  = 

Is  there  any  uniformity  in  the  value  of  these  ratios? 
Do  your  results  afford  further  evidence  of  the  law  of 
;  definite  proportions  ?     If  so,  in  what  way  ? 

6.  The  Law  of  Multiple  Proportions.  —  We  have  learned 
that  when  two  or  more  elements  unite  to  form  a  compound 
they  do  so  in  a  constant  ratio.     We  have  seen,  however, 
that  the  same  two  or  three  elements  may  unite  to  form 
several  compounds,  and  at  first  this  may  seem  contrary  to 
the  statement  of  the  preceding  law.     It  is  a  modification, 
but  not  a  contradiction.     If  a  new  and  different  compound 
is  formed  when  other  proportions  are  used,  in  this  the 
quantity  of  the  elements  that  enter  into  combination  is 
always  some  multiple  of  the  lowest.     An  illustration  will 
make  this  plain.     Thus,  we  are  familiar  with  the  series  of 
nitrogen  oxides  :  — 


162 


MODERN  CHEMISTRY 


Nitrogen  Monoxide 
"         Dioxide  . 
"         Trioxide 
"        Tetroxide 
"         Pentoxide 


N20 
N202 

N203 
N204 
N206 


F2:O 
L:0fl 


'2  * 


28:16 

28:32 
28  :  48 
28:64 
28:80 


It  is  seen  that  while  the  weight  of  the  nitrogen  entering 
into  combination  remains  constant,  the  oxygen  is  in  the 
ratio  of  2,  3,  4,  and  5  times  what  it  is  in  the  lowest  of  the 
series. 

7.  This  law  may  be  proved  experimentally  by  estimat- 
ing the  amount  of  oxygen  that  a  given  weight  of  potas- 
sium chlorate,  KC1O3,  will  yield,  by  the  method  previously 
suggested.  Then,  determine  the  amount  in  potassium 
perchlorate,  KC1O4.  In  these  two  compounds  we  should 
find  the  ratio  to  agree  with  that  expressed  in  the  formulae, 
that  is,  3  and  4  times  what  would  be  contained  in  a  mole- 
cule like  mercuric  oxide,  HgO. 


FIG.  44. 

EXPERIMENT  105.  —  To  prove  the  law,  the  work  may  be  conven- 
iently done  as  shown  in  the  accompanying  figure.  Instead  of  the 
flask,  0,  a  hard-glass  test-tube  may  be  used.  Put  into  the  flask  about 
1  g.  of  manganese  dioxide,  MnO2,  and  weigh  carefully  the  flask  and 


FUNDAMENTAL  LAWS  OF  CHEMISTRY  163 


contents.  Then  add  to  it  about  1J  g.  of  potassium  chlorate, 
and  weigh  accurately.  The  difference  will  be  the  chlorate.  A  is  a 
liter  bottle  fitted  with  a  two-hole  rubber  cork.  The  delivery  tube,  d, 
just  reaches  through  the  corks  of  O  and  A.  The  tube,  e,  should  be 
made  in  two  parts,  joined  by  rubber  tubing  several  inches  long,  and 
should  reach  nearly  to  the  bottom  of  both  A  and  B.  A  pinch  clamp 
will  be  needed  at  e.  Xearly  fill  A  with  water,  and  by  suction  the 
tube  connecting  A  and  B,  completely.  Fasten  the  clamp  at  e.  See 
that  the  corks  fit  air-tight,  and  fill  B  to  the  same  height  as  A.  Open 
the  clamp  an  instant,  then  empty  B.  Replace  5,  remove  the  clamp, 
and  heat  the  chlorate  carefully  until  water  is  no  longer  driven  out  of 
A.  Let  the  tube  cool,  equalize  the  pressure  in  the  two  bottles  as  in 
Experiment  37,  and  again  fasten  the  clamp.  Determine  the  volume 
of  water  in  B  ;  this  will  give  the  volume  of  the  oxygen  at  the  tempera- 
ture and  pressure  of  the  room.  According  to  methods  already  given 
on  page  96,  reduce  this  volume  to  what  it  would  be  under  standard 
conditions.  Knowing  the  weight  of  a  liter  of  oxygen,  1.43  g.,  find  the 
weight  of  the  determined  volume.  Weigh  also  the  cooled  flask,  O,  and 
determine  its  loss  ;  this  also  represents  the  oxygen. 

Next,  arrange  the  apparatus  as  at  the  beginning.  Into  the  hard- 
glass  tube  put  about  1..4  g.  of  potassium  perchlorate,  KC1O4,  and,  after 
making  connections,  heat  strongly  as  before  until  no  more  gas  is  pro- 
duced. Cool  and  weigh  the  flask  or  tube  ;  the  loss  will  represent  the 
oxygen,  which  may  be  checked  up  by  determining  the  volume  of 
the  gas  given  off  as  before  and  reducing  to  standard  conditions. 
Let  the  student  now  compare  results.  The  two  reactions  are  as 
follows  :  — 

KC103  -f  heat  =  KC1  +  3  O, 

and  KC1O4  +  heat  =  KC1  +  4  O. 

From  other  experiments  we  know  that  the  oxygen  is  entirely  removed 
and  that  potassium  chloride,  KC1,  remains.  Then  we  should  have  the 
proportion 

Mol.  wt.  KC1O3  :  wt.  of  O  in  1  mol.  KC1O3  :  :  1.25  g.  :  m  g., 
in  which  m  =  no.  grams  found  by  experiment  above.    Substituting, 
122.5  :  x  :  :  1.25  g.  :  m  g., 

_  m  x  122.5 
1.25 


164  MODERN  CHEMISTRY 

Then,  as  16  is  the  weight  of  one  atom  of  oxygen,  there  would  be  as 
many  atoms  of  oxygen  in  the  molecule  as  16  is  contained  times  in  x ; 
the  result  should  agree  very  closely  with  the  assumed  number. 
In  the  same  way, 

Mol.  wt.  KC1O4 :  wt.  of  O  in  1  mol.  KC1O4 : :  1.40  g. :  n  g., 
in  which  n  =  no.  grams  found  in  second  instance  above.    Or, 
138.5  :  y  : :  1.40  g. :  n  g., 

_  n  x  138.5 

1.40 
How  does  the  value  of  y  agree  with  the  known  value? 

8.  Combining  Weights.  —  We  have  previously  learned 
that  when  elements  or  compounds  react  with  each  other 
in  the  formation  of  new  substances,  they  always  do  so  in 
a  fixed  or  definite  proportion.  We  have  seen  also  that 
when  several  compounds  are  formed  from  the  same  two 
elements,  there  is  one  smallest  quantity  of  which  all  the 
others  are  multiples.  This  smallest  amount  in  the  case  of 
the  nitrogen  oxides  was  found  to  be  16  for  the  oxygen, 
and  all  the  others  were  multiples  of  this.  Therefore,  16 
is  regarded  as  the  atomic  weight  of  oxygen,  and  in  all 
chemical  reactions  into  which  it  enters,  this,  or  some 
multiple  of  it,  is  its  combining  weight. 

EXPERIMENT  106.  —  To  find  the  combining  weight  of  copper.  Put 
into  a  beaker  2|  g.  of  clean,  bright  copper,  accurately  weighed,  and 
dissolve  slowly  in  nitric  acid  somewhat  diluted.  Use  every  precaution 
to  prevent  loss  by  spurting,  just  as  in  other  similar  work,  and  when 
the  copper  is  all  dissolved,  transfer  the  solution  to  a  weighed  evapo- 
rating dish,  as  small  as  will  conveniently  hold  the  solution ;  carefully 
rinse  off  the  cover-glass  and  the  beaker  into  the  evaporating  dish,  and 
evaporate  to  dryness.  We  now  have  a  blue  salt,  copper  nitrate.  Be 
sure  it  is  perfectly  dry,  and  then  remove  the  sand-bath,  or  any  other 
protection  used  for  the  dish,  and  gradually  increase  the  heat  until  all 
particles  of  the  blue  salt  have  been  changed  to  a  black  compound.  A 
dull  red  heat  is  generally  necessary  for  this.  We  now  have  copper 


FUNDAMENTAL  LAWS  OF  C&EMISTRY        165 

oxide,  CuO.  Cool  and  weigh  carefully.  Determine  how  much  oxygen 
has  combined  with  the  copper  by  subtracting  the  amount  of  copper 
used  from  the  weight  of  oxide  obtained. 

Dish  +  CuO  .       —    m  +  x ;  m  =  wt.  of  dish ;  x,  of  CuO. 
Dish  +  Cu     .  m  +  n; .  n  =  wt.  of  Cu  =  2±  g. 

O m  +  x  -  (m  +  n)  =  y. 

Numerous  experiments  have  shown  that  the  combining  weight  of 
oxygen  is  16 ;  using  this  as  a  basis,  we  can  determine  what  it  is  for 
copper : — 

Wt.  of  O  found  :  wt.  of  Cu  used  : :  comb.  wt.  of  O  :  comb.  wt.  of  Cu. 
or,  Wt.  of  O  :  2J  g.  Cu  : :  16  :  z. 

From  this  proportion  the  combining  weight  of  copper  should  be  found 
to  be  approximately  what  is  given  in  the  table  on  page  9.  The  sources 
of  error  are  liable  to  make  the  difference  comparatively  great,  but  the 
result  should  not  vary  too  much. 

EXPERIMENT  107.  —  Purpose,  same  as  above.  Use  3  or  4  g.  of 
finely  powdered  copper  nitrate  which  has  not  been  exposed  to  the  air 
any  length  of  time.  Be  sure  the  exact  weight  is  known,  then  heat 
in  a  small  evaporating  dish,  or  better,  in  a  porcelain  crucible,  cautiously 
at  first ;  when  the  nitrate  is  converted  into  the  black  oxide  as  before, 
cool  and  find  the  weight.  Experiment  has  shown  that  1  g.  of  crystal- 
lized copper  nitrate  contains  0.2619  g.  of  metallic  copper.  From  this 
determine  the  amount  of  copper  represented  by  the  3  g.  (or  4  g.)  of 
nitrate  used. 


Wt.  of  dish  +  CuO      ...:...        — 

Wt.  of  dish 

CuO 

Cu 

O 

Wt.  of  O  :  wt.  of  Cu  : :  16  :  x. 

Does  this  give  practically  the  same  combining  weight  for  copper 
that  the  preceding  did?  If  the  results  do  not  correspond  fairly  well 
with  each  other  and  with  the  table,  the  experiments  should  be  repeated. 
EXPERIMENT  108.  —  To  find  the  combining  weight  of  tin.  For  this 
use  granulated  tin.  If  not  at  hand,  procure  a  quantity  of  pure  tin 


166  MODERN  CHEMISTRY 

foil,  melt  it  in  an  iron  ladle,  and  pour  into  cool  water.  Remove  from 
the  water  and  dry  it,  when  it  will  be  ready  for  use.  Weigh  out  care- 
fully 2  g.  of  the  granulated  tin,  and  treat  with  nitric  acid  in  an  evapo- 
rating dish.  Take  care  always  to  avoid  loss  by  spurting.  Evaporate 
slowly  to  dry  ness,  and  then  gradually  heat  the  white  residue  to  dull 

redness. 

Wt.  of  dish  +  SnO2 .         

Wt.  of  dish 

SnO2 

Wt.  of.  Sn 

02 — 

It  has  been  found  by  analysis  that  the  amount  of  oxygen  in  this 
compound  indicates  two  atoms  to  the  molecule,  hence  in  making  our 
calculations  that  amount  must  be  used.  Then  we  have  — 

wt.  of  O  found  :  wt.  of  Sn  used  : :  32  (2  x  16)  :  x. 

EXPERIMENT  109.  —  Repeat  the  above  experiment,  using  2|  or  3  g. 
of  tin,  and  make  calculations  as  before. 

How  do  the  results  in  the  two  experiments  agree  ?  If  they  do  not 
correspond  fairly  well  with  the  atomic  weight  given  in  the  table, 
allowing  for  errors  in  weighing,  the  experiment  should  be  repeated. 

9.  Such  experiments  as  the  above  might  be  endlessly 
multiplied.  We  have  found  in  these,  as  has  been  the 
case  in  an  indefinite  number  of  instances  in  which  chem- 
ists have  done  the  work  with  the  utmost  care,  that  every 
element  combines  with'  others  in  some  exact  proportion 
by  weight,  and  whether  we  use  much  or  little  of  the 
element,  in  the  same  compound  the  ratio  never  changes. 
This  fact  is  of  the  utmost  importance,  for  upon  it  depends 
much  of  the  science  of  chemistry.  It  is  this  that  enters 
into  the  application  of  chemistry  to  the  arts  and  manufac- 
tures, and  renders  its  results  so  sure  and  unchanging. 

10.  Some  Application  of  the  Laws  of  Combination.  — 
Knowing  that 'the  laws  of  combination  are  true,  we  may 
make  use  of  the  principles  in  determining  the  strength 


FUNDAMENTAL  LAWS  OF  CHEMISTRY  167 

of  acid  or  alkaline  solutions.  The  following  work  will 
illustrate  this. 

EXPERIMENT  110.  —  To  determine  the  strength  of  any  hydrochloric 
acid  solution  in  the  laboratory.  Put  the  acid  to  be  tested  into  a 
burette  and  take  the  reading.  From  this  allow  10  cc.  to  flow  into  an 
evaporating  dish,  add  a  drop  or  two  of  litmus  or  phthalein,  and  then, 
from  another  burette,  after  taking  the  reading,  run  in  a  solution  of 
caustic  soda  until  the  solution  in  the  evaporating  dish  is  neutralized, 
as  in  previous  work.  Evaporate  slowly  to  dryness,  cool,  and  weigh. 
Subtract  the  weight  of  the  dish  to  determine  the  salt  obtained.  Sup- 
pose this  is  0.585  g.  Now  we  know  that  caustic  soda  and  hydrochloric 
acid  react  with  each  other  according  to  the  following  equation :  — 

NaOH  +  HC1  =  NaCl  +  H2O. 

From  this  we  see  that  one  molecule  of  pure  hydrochloric  acid  yields 
one  of  sodium  chloride,  or  36.5  parts  by  weight  of  acid  give  58.5  of 
salt.  The  0.585  g.  of  salt  would  thus  correspond  to  0.365  g.  of  acid, 
the  amount  in  10  cc.  of  the  solution  used.  Then  in  a  liter,  1000  cc., 
there  would  be  100  times  this  amount,  or  36.5  g.  of  pure  acid.  The 
liter  of  acid  then  ought  to  weigh  1000  g.  -f  36.5  g.  =  1036.5  g.  The 
question  simply  is  this :  36.5  g.,  the  amount  of  pure  acid,  is  what 
per  cent  of  1036.5  g.,  the  weight  of  the  acid  solution  ?  This  is  found 
to  be  about  3£  per  cent. 

EXPERIMENT  111.  —  Repeat  the  preceding  experiment,  neutralizing 
10  cc.  of  the  hydrochloric  acid  with  caustic  potash.  Make  your  cal- 
culations from  the  following  equation  :  — 

KOH  +  HC1  =  KC1  +  H2O. 

Do  your  results  agree  with  the  preceding  as  to  the  per  cent  strength 
of  acid? 

11.  To  determine  the  Amount  of  Caustic  Soda  or  Potash 
in  the  Solutions  used  above.  —  We  know  that  when  an  acid 
and  an  alkali  are  put  together,  they  neutralize  each  other 
to  form  a  salt.  If  then  we  know  how  much  acid  is  con- 
tained in  a  solution,  and  measure  the  amount  of  the  latter 
used,  having  some  means  of  knowing  when  the  alkali  is 


168  MODERN  CHEMISTRY 

exactly  neutralized,  we  can  easily  calculate  the  amount  of 
alkali  contained  in  a  given  volume  of  solution. 

EXPERIMENT  112.  —  Suppose  we  are  required  to  determine  the 
number  of  grams  of  sodium  hydroxide  in  1  liter  of  the  solution.  We 
know  the  reaction  is 

NaOH  +  HC1  =  NaCI  +  H2O, 
or  by  weight,  40      +  36.5  =  58.5  +   18. 

That  is,  40  g.  of  caustic  soda  are  necessary  to  neutralize  36.5  g.  of 
hydrochloric  acid.  Suppose  now  we  have  a  solution  of  acid  that  con- 
tains 3.65  g.  of  pure  hydrochloric  acid  to  the  liter,  then 

1000  cc.  HC1  would  neutralize  4.0  g.  of  NaOH. 

Then,  if  with  100  cc.  of  caustic  soda  solution  we  used  20  cc.  of  the 
acid  solution,  we  should  have  this  proportion  :  — 

1000  cc.  HC1 :  4.0  g.  NaOH  : :  20  cc.  HC1 :  x  g.  NaOH ; 

x  =  .08. 

That  is,  in  100  cc.  of  the  solution  of  caustic  soda  there  are  .08  g.  of 
the  solid  alkali  dissolved ;  then  in  1  liter  there  would  be  10  times  as 
much,  or  .8  g. 

For  such  work  as  this  we  very  often  use  oxalic  acid  instead  of 
hydrochloric,  because  it  is  easy  to  weigh  out,  and  forms  a  good 
working  solution.  Its  formula  is  H2C2O4,  2  H2O.  With  caustic  soda 
the  reaction  is 

2  H2O,  H2C2O4  +  2  NaOH  =  Na2C2O4  +  4  H2O, 
or  by  weight,  126       +       80       =134          +72. 

That  is,  126  g.  of  oxalic  acid  will  neutralize  80  g.  of  caustic  soda. 
Suppose  for  work  we  weigh  out  6.3  g.  of  oxalic  acid  and  dissolve  in 
1000  cc.  of  pure  water.  This  will  be  our  standard  solution  of  acid. 

To  find  how  much  caustic  soda  in  1  liter  of  solution.  Measure  out 
accurately  into  a  beaker  50  cc.  of  the  alkali  solution,  and  add  one  drop 
of  phenolphthalein,  or  about  1  cc.  of  litmus  solution.  Next  take  the 
reading  of  a  burette  containing  the  standard  oxalic  acid  solution,  and 
with  constant  stirring  let  the  acid  drop  in  slowly  until,  finally,  by  the 
addition  of  a  single  drop  the  red  color  of  the  phenol  disappears,  or  the 


FUNDAMENTAL  LAWS  OF  CHEMISTRY  169 

blue  of  the  litmus  changes  to  red.  Again  read  the  burette  and  deter- 
mine how  much  acid  has  been  used.  Suppose  it  has  been  10  cc.  Then 
to  calculate, 

1000  cc.  acid  •  4.0  g.  NaOH  : :  10  cc. :  x  NaOH ; 
x  =  .04  g.  NaOH, 

the  amount  in  50  cc.  of  NaOH  solution  used.  In  1000  cc.  there  would 
be  20  times  as  much,  or  .8  g. 

PROBLEM  1.  —  Let  the  teacher  make  up  a  solution  of  caustic  potash 
with  distilled  water,  and  have  the  student  determine  the  number  of 
grams  used  to  the  liter. 

PROBLEM  2. —  In  the  same  way  let  the  student  determine  the 
amount  of  common  salt  in  a  solution  by  using  in  the  burette  a 
solution  of  silver  nitrate  containing  17  g.  per  liter.  To  determine 
when  sufficient  silver  nitrate  is  used,  add  to  the  common  salt  solution 
sufficient  potassium  chromate  solution  to  give  a  yellow  color.  With 
constant  stirring  run  in  the  silver  nitrate  until  the  precipitate  that 
forms  shows  the  faintest  red  tinge.  The  reaction  is 

NaCl  +  AgNO,  =  AgCl  +  NaNO3, 
or  by  weight,         58.5  +     170      =  143.5  +      85. 

That  is,  170  g.  of  silver  nitrate  will  precipitate  the  chlorine  in  58.5  g. 
of  salt,  or  if  17  g.  of  silver  nitrate  were  used  to  make  a  liter  of  the 
solution,  then  1000  cc.  of  silver  nitrate  would  precipitate  the  chlorine 
in  5.85  g.  of  salt.  Or, 

1000  cc.  AgNO3  :  5.85  g.  NaCl : :  m  cc.  AgNO3  •  x  g.  NaCl, 

in  which  m  is  the  number  of  cubic  centimeters  of  silver  nitrate  solu- 
tion used  with  the  amount  of  common  salt  solution  taken.  If  this 
latter  is  20  cc.,  or  ^  of  a  liter,  then  50  m  =  number  cubic  centimeters 
AgNO3  necessary  to  precipitate  the  chlorine  in  1  liter. 

12.  Displacing  Power  of  Metals.  —  We  have  seen  in  pre- 
paring hydrogen  that  various  metals  have  the  power  of 
reacting  with  certain  acids  to  displace  the  hydrogen 
contained.  Of  course  this  displacing  power  is  in  accord- 
ance with  the  valence  of  the  element  (see  chapter  on 


170  MODERN  CHEMISTRY 

Valence),  and  the  following  plan  may  be  used  to  deter- 
mine it :  — 

EXPERIMENT  113.  —  Let  a  part  of  the  students  perform  this  experi- 
ment, another  portion  No.  114,  and  another,  115.  Arrange  apparatus 
as  for  Experiment  37  or  105.  Use  a  wide-mouth, 
4  oz.  bottle  instead  of  a  flask  or  hard  glass  tube. 
Put  into  this  1  g.  of  finely  granulated  zinc  and 
a  short  test-tube  containing  15  or  20  cc.  strong 
hydrochloric  acid.  Make  connections  air-tight. 
Fill  the  delivery  tube  with  water  and  equalize 
pressure  in  the  two  bottles  as  in  other  experi- 
ments. When  all  is  ready,  tip  the  generating 
bottle  so  that  the  acid  shall  be  spilled  upon  the 
FIG.  45.  zinc.  When  the  zinc  has  disappeared  and  the 

generator  has  cooled,  equalize  the  pressure  in 

the  two  bottles  and  attach  the  clamp.  Measure  the  water  expelled. 
Assuming  this  to  be  the  volume  of  the  hydrogen  displaced  from  the 
acid  by  1  g.  of  zinc,  allow  for  vapor  tension  and  reduce  to  standard 
conditions.  Suppose,  for  example,  it  is  found  that  m  cc.  of  water  have 
been  forced  over  by  the  hydrogen,  and  that  by  reducing  this  volume 
to  standard  conditions,  we  obtain  n  cc.  as  a  result,  then  as  1  liter 
of  hydrogen  weighs  .0896  g.,  n  cc.  would  weigh 

n  x  .0896  ,  ,     , 

10QQ      =  w  g.  of  hydrogen. 

Then  we  should  have  the  proportion 

w  g.  of  H  :  1  g.  of  Zn  : :  x  :  65 ; 

that  is,  the  weight  of  the  hydrogen  obtained  is  to  the  weight  of  the 
zinc  used  in  displacing  it  as  x  is  to  65,  the  atomic  weight  of  zinc. 
This  should  give  for  the  value  of  x,  approximately,  2.  Then  as  the 
hydrogen  atom  is  the  standard,  or  1,  in  this  case  x  represents  the 
weight  of  two  atoms  of  hydrogen.  In  other  words,  the  zinc  atom  has 
the  power  of  displacing  two  atoms  of  hydrogen. 

EXPERIMENT  114.  —  AVith  apparatus  arranged  as  in  the  preceding 
experiment,  let  the  student  use  one  gram  of  aluminum  wire  cut  into 
small  pieces.  No  heat  will  be  necessary  if  strong  hydrochloric  acid 
be  used,  and  the  chemical  action,  slow  at  first,  will  soon  become  very 
rapid.  Determine  as  before  the  volume  and  weight  of  the  hydrogen 
set  free.  Then  we  have 


8ULPHV&  AND  ITS  COMPOUNDS  171 

• 

wt.  of  H  obtained  :  wt.  of  Al  us  d : :  x :  27,  atomic  wt.  of  Al, 

and  x  -  ? 

From  this  what  can  you  say  is  the  displacing  power  of  the  aluminum 
atom? 

EXPERIMENT  115.  —  In  exactly  the  same  way  try  1  gram  of  magne- 
sium ribbon,  cut  into  small  pieces.  Hydrochloric  acid  somewhat 
diluted  had  better  be  used,  as  the  action  is  very  rapid.  Make  your 
corrections  for  temperature  and  pressure,  and  calculate  as  before. 
What  do  you  find  for  the  displacing  power  of  the  magnesium  atom  ? 

SUMMARY  OF  CHAPTER 

Statement  of  Law  of  Definite  Proportions. 

Experiments  illustrating  it. 
Law  of  Multiple  Proportions. 

How  illustrated. 
Combining  weights. 

Method  of  determining  by  experiment. 
For  copper. 
For  tin. 
Practical  application. 

Method  of  determining  amount  of  acid  or  alkali  in  a  solution. 

Method  of  determining  valence  or  displacing  power  of  metals. 


.CHAPTER  XIII 

SULPHUR  AND  ITS  COMPOUNDS 

1.  Where  found.  —  Sulphur  is  an  element  that  has  been 
known  from  very  early  times.  By  some  of  the  alchemists 
it,  together  with  mercury,  was  regarded  as  forming  all  of 
the  metals. 

It  is  a  native  of  volcanic  regions,  and  is  found  in  abun- 
dance in  Sicily  and  to  some  extent  in  Iceland.  There  are 
said  to  be  some  deep  deposits  in  the  Southern  States,  but 


172 


MODERN  CHEMISTRY. 


they  have  not  been  developed.  In 'the  form  of  compounds 
with  the  metals,  sulphur  is  found  abundantly  and  very 
widely  distributed.  Some  of  the  more  common  compounds 
are  gypsum,  CaSO4,2H2O,  iron  pyrite,  FeS2,  galena, 
PbS,  and  zinc  blende,  ZnS.  In  the  form  of  hydrogen  sul- 
phide, it  is  found  in  many  mineral  springs  and  is  often 
emitted  from  volcanoes. 

2.  For  many  years  Sicily  had  a  monopoly  of  the  sul- 
phur trade.  It  occurs  there  in  almost  unlimited  quan- 
tities, mixed  with  earthy  matter.  This  mixture  may  be 
partially  purified  by  a  method  similar  to  that  employed 
in  the  preparation  of  charcoal.  Large  piles  of  the  crude 
sulphur  are  heaped  up  and  covered  with  earth  and  sod. 


FIG.  46. 


The  mass  is  then  ignited  and  a  part  of  the  sulphur  in 
burning  melts  the  remainder,  which  runs  out  into  trenches 
or  vats,  leaving  the  earthy  matter  behind. 


8ULPHUE  AND  ITS  COMPOUNDS  173 

3.  For  many  purposes  the  sulphur  thus  obtained  needs 
further  purification.     It  is  heated  and  vaporized  in  retorts, 
the  vapors  passing  over  into  cool  chambers  and  condensing 
upon  the  walls  in  the  form  known  as  flowers  of  sulphur. 
If  the  operation  continues  for  a  length  of  time,  however, 
the  walls  become  heated  enough  to  melt  the  sulphur  that 
forms  upon  them.     It  is  then  allowed  to  run  out  into 
molds,  in  which  form  it   is  known  as  brimstone  or  roll 
sulphur.     (See  Fig.   46.)     S  is  a  cylinder  in  which  the 
sulphur  is  melted,  V,  a  retort  where  it  is  vaporized,  and 
E,  the  condensing  chamber. 

4.  New  Source  of  Supply.  —  From  the  fact  that  Sicily 
controlled  the  sulphur  trade,  prices  rose  so  high  at  one 
time   that   the    English   manufacturers   were   obliged  to 
resort   to   some   other   source   of   supply.     Sulphur   was 
used  extensively  in  making  sulphuric  acid  for  the  manu- 
facture of  soda  crystals.     It  was  found  that  by  roasting 
iron  pyrite,  FeS2,  a  compound  that  had  been  hitherto  alto- 
gether worthless,  the  sulphur  dioxide  could  be  obtained ; 
or  if  the  ore  was  heated  in  retorts  sealed  up  to  prevent 
access  of  air,  the  sulphur  was  not  oxidized,  and  could 
be  condensed.     As  the  pyrite  is  very  abundant,  and  the 
method  of  obtaining  the  sulphur  cheap,  this  at  the  present 
time  furnishes  not  only  about  all  the  sulphur  needed  in 
making  sulphuric  acid,  but  even  more,  so  that  the  demand 
for  Sicilian  sulphur  has  greatly  decreased.     The  reaction 
that   takes   place  when  iron  pyrite  is  heated  in   sealed 
retorts  is          g  ^  +  heat  =  2  S  +  Fe3S4. 

5.  Characteristics  of  Sulphur.  —  Sulphur  is  a  yellow, 
brittle  solid,  twice  as  heavy  as  water.      It  is  seen  in  a 
number  of  forms,  of  which  the  flowers  and  roll  sulphur 
have  been  mentioned.     It  also  occurs  crystallized. 


174  MODERN  CHEMISTRY 

EXPERIMENT  116.  —  Into  a  test-tube  put  about  a  cubic  centimetei 
of  carbon  disulphide,  and  add  a  little  sulphur.  When  the  latter  has 
dissolved,  pour  off  the  clear  solution  upon  a  watch  crystal,  and  allow 
it  to  evaporate  slowly  to  dryness.  The  sulphur  will  form  in  crystals, 
the  shape  of  which  may  be  recognized  if  the  evaporation  is  slow.  If 
necessary,  however,  examine  with  a  magnifying  glass.  What  form 
have  they  ? 

EXPERIMENT  117.  —  Fill  a  small  crucible  nearly  full  of  sulphur, 
and  heat  till  it  is  melted.  Allow  it  to  cool,  and  when  a  crust  has 
formed  over  the  surface,  break  an  opening  in  the  top  and  pour  out 
what  remains  molten.  Let  it  cool  a  little  more  and  break  open  the 
mass.  What  kind  of  crystals  have  formed? 

EXPERIMENT  118.  — Put  4  or  5  g.  of  sulphur  into  a  test-tube  and 
warm.  Note  how  it  changes,  first  melting  to  form  a  light  yellow- 
colored  liquid,  then  becoming  quite  thick  again  and  very  dark,  then 
thin  again.  At  this  last  stage,  pour  out  the  sulphur  into  cold  water 
and  note  its  condition.  This  is  called  amorphous  sulphur,  or  some- 
times plastic  sulphur. 

6.  Sulphur  is  found  in  a  large  variety  of  crystallized 
forms.     The  octahedral  and  the  long,  needle-like  crystals 
have   been  seen.      Upon   standing   for  some  time  these 
gradually  change  into  other  forms,  modifications  of  the 
two.      Amorphous   sulphur   is    dark-colored  and  elastic, 
somewhat  like  rubber.      It  is  regarded  as  an  allotropic 
form.     Sulphur  is  insoluble  in  water,  hence  has  no  taste  ; 
it  is  also  without  odor.     As  we  have  seen,  it  is  soluble  in 
carbon  disulphide.     It  is  combustible,  burning  with  a  pale 
blue  flame,  and  forming  the  well-known  irritating  gas, 
sulphur  dioxide.     At  high  temperatures  sulphur  combines 
readily  with  most  of  the  metals,  forming  sulphides.     This 
has  been  shown  already  in  preparing  ferrous  sulphide  by 
heating  iron  filings  mixed  with  sulphur.     Copper  turnings 
serve  equally  well. 

7.  Comparison  of  Ozone  with  Allotropic  Sulphur.  —  In 
the  case  of  ozone,  we  have  seen  that  its  molecule  is  differ- 


SULPHUR  AND  ITS  COMPOUNDS  175 

ent  from  that  of  the  oxygen  molecule.  The  same  is  be- 
lieved to  be  true  of  sulphur  arid  its  allotropic  form,  as  well 
as  of  all  other  elements  which  show  the  same  variation. 
We  cannot  prove  this  for  sulphur,  but  there  are  some 
facts  which  make  this  theory  strongly  plausible.  Thus, 
if  the  vapor  is  weighed  at  1000°  temperature,  it  is  only 
one-third  as  dense  as  when  weighed  at  500°. 

8.  Uses  of  Sulphur. — Sulphur  is  used  largely  in  the 
manufacture  of   gunpowder,  the  other  two  constituents 
being  charcoal  and  saltpeter.  '  These  are  united  in  about 
the  following  proportions  :  — 

Sulphur 12  per  cent 

Charcoal 13       " 

Saltpeter 75       " 

"  Greek  fire,"  which  played  so  important  a  part  in  the 
early  centuries,  and  the  composition  of  which  was  kept  a 
secret  for  several  hundred  years,  differed  very  little  from 
the  gunpowder  of  the  present  time.  Sulphur  is  employed 
to  some  extent  in  the  manufacture  of  rubber  goods,  espe- 
cially vulcanite,  and  considerably  in  fumigating  buildings; 
it  is  used  largely  in  making  sulphuric  acid.  Because  of 
its  low  kindling-point  sulphur  has  been  used  very  exten- 
sively in  the  manufacture  of  matches,  but  the  irritating  gas 
produced,  and  the  slowness  with  which  such  matches  burn, 
have  led  to  the  substitution  of  other  substances. 

COMPOUNDS  OF  SULPHUR 

9.  Hydrogen  Sulphide,  H2S.  —  This  gas,  known  also  as 
sulphureted  hydrogen,  occurs  in  many  mineral  springs, 
which  give  it  off  abundantly;    it  is  sometimes  emitted 
from  volcanoes,  and  is  noticed  in  the  decay  of  eggs  and 
other  similar  substances. 


176  MODERN  CHEMISTRY 

10.  How  prepared.  —  For  laboratory  purposes  hydrogen 
sulphide  is  always  prepared  by  treating  ferrous  sulphide, 
FeS,  with  sulphuric  acid. 

EXPERIMENT  119.  —  Owing  to  the  offensive  odor  of  the  gas,  it  should 
be  prepared  in  very  small  quantities,  and  kept  from  access  to  the  room 
as  much  as  possible.  Put  into  a  test-tube  a  small  bit  of  ferrous  sul- 
phide, cover  it  with  water,  and  add  a  few  drops  of  strong  sulphuric 
acid.  Action  will  begin  at  once.  Notice  the  odor  of  the  gas.  Has 
it  any  color  ?  Attach  a  jet  and  ignite  it.  With  what  kind  of  a  flame 
does  it  burn  ?  Notice  the  odor  given  off  by  the  burning  gas.  Hold  a 
cold  beaker  over  the  flame.  What  do  you-  see  depositing  upon  it? 
What  are  the  two  products  formed  when  hydrogen  sulphide  burns? 
Write  the  reaction. 

The  reaction  that  takes  place  when  hydrogen  sulphide  is  prepared 
is  seen  below  :  — 

FeS  +  H2SO4  =  FeSO4  +  II2S, 

9  FeS  +  2  HC1  =  FeCl2  +  H2S. 

Hydrochloric  acid  may  be  used  instead  of  sulphuric  acid  with  good 

results. 

11.  Characteristics  of  Sulphureted  Hydrogen.  —  It  is  a 

colorless  gas,  having  a  very  disagreeable,  nauseating  odor ; 
is  somewhat  poisonous,  and  should  not  be  inhaled.  It  is 
inflammable,  burning  with  a  bluish  flame,  is  a  little 
heavier  than  air,  and  somewhat  soluble  in  water.  It  has 
the  power  of  forming  precipitates  with  solutions  of  many 
metallic  salts. 

EXPERIMENT  120.  —  Into  a  test-tube  put  a  little  of  a  mercuric 
chloride  solution,  into  another  a  solution  of  antimony  tartrate,  into 
a  third  arsenic  trioxide  dissolved  in  hydrochloric  acid  and  water. 
Attach  a  delivery  tube  to  a  hydrogen  sulphide  generator,  and  pass  the 
gas  through  each  of  the  solutions.  Notice  the  color  of  the  precipitates 
obtained.  Lead  salts  are  very  sensitive  to  the  action  of  hydrogen 
sulphide,  and  are  used  in  testing  for  its  presence. 

12.  Use  of  Hydrogen  Sulphide.  —  Mineral  waters  con- 
taining this  gas  in  solution  are  supposed  to  be  beneficial 


SULPHUR  AND  ITS  COMPOUNDS  177 

co  health.  With  this  exception,  about  the  only  use  for 
hydrogen  sulphide  is  in  the  laboratory,  as  a  reagent,  espe- 
cially in  making  analyses  of  unknown  solutions.  Many 
of  the  metals  in  the  form  of  salts  are  converted  by  hydro- 
gen sulphide  into  insoluble  sulphides.  Such  metals,  there- 
fore, when  treated  with  the  gas,  may  be  separated  from 
others  which  are  not  so  precipitated. 

EXPERIMENT  121.  —  The  above  statements  will  be  made  plain  by 
this  experiment.  Into  a  beaker  put  a  few  cubic  centimeters  of  a  solu- 
tion of  mercuric  nitrate  and  as  much  of  zinc  sulphate ;  add  a  few  drops 
of  hydrochloric  acid,  and  pass  through  it  a  current  of  sulphureted 
hydrogen  until  the  odor  of  the  gas  is  still  perceptible  after  shaking 
the  solution.  Then  filter  out  the  black  precipitate  and  test  the  clear 
filtrate  for  zinc  with  ammonia,  as  you  have  done  in  Chapter  VII,  Sec- 
tion 12.  Have  you  succeeded  in  separating  the  two  metals  ? 

13.  Oxides  of  Sulphur.  —  There  are  two  of  these  com- 
pounds, the  dioxide  and  the  trioxide,  SO2  and  SO3.     It 
is  only  the  first  that  is  of  special  importance  or  interest 
to  us. 

14.  Sulphur  Dioxide,  S02.  —  This  is  also  known  as  sul- 
phurous anhydride,  because  by  passing  it  into  water  sul- 
phurous acid  is  formed.     It  is  the  familiar,  irritating  gas 
always  produced  when  sulphur  is  burned  in  the  air. 

15.  How  prepared. — For  laboratory  purposes  sulphur 
dioxide   is   prepared   by   treating   copper   turnings   with 
strong  sulphuric  acid.     The  reaction  is  usually  indicated 
as  follows :  — 

Cu  +  2  H2S04  =  CuSO4  +  2  H2O  +  SO2. 

If  this  is  compared  with  the  reaction  of  zinc  and  sulphuric 
acid  upon  each  other,  it  will  be  seen  to  be  very  different. 
Zinc  is  acted  upon  by  cold,  dilute  acid,  while  copper  re- 


178  MODERN  CHEMISTRY 

quires  the  acid  hot  and  concentrated.     It  is  probable  that, 
as  with  zinc,  hydrogen  is  first  formed,  thus  :  — 

Cu  +  H2SO4  =  H2  +  CuSO4, 

and  that  this  nascent  hydrogen  immediately  attacks  an- 
other molecule  of  sulphuric  acid,  decomposing  it,  thus :  — 

H2S04+H2=2H20  +  S02. 

Putting  these  two  reactions  together,  we  have  the  one 
given  above. 

EXPERIMENT  122.  —  Put  into  a  test-tube  a  few  copper  turnings  and 
nearly  cover  with  strong  sulphuric  acid.  Heat  moderately  until  the 
fumes  begin  to  come  off,  and  collect  two  or  three  bottles  of  the  gas  as 
you  have  carbon  dioxide,  by  downward  displacement.  What  is  the 
odor  of  the  gas  ?  Test  it  to  learn  whether  it  will  support  combustion 
or  will  burn.  What  can  you  say  of  its  density  ?  Try  its  effect  upon 
moistened  red  and  blue  litmus  paper ;  state  results.  Pour  into  one 
bottle  of  the  gas  a  few  cubic  centimeters  of  litmus,  cochineal,  or  some 
other  vegetable  solution,  and  shake  it.  What  happens?  Suspend  in 
another  bottle  some  colored  paper,  or  silk  or  straw  goods,  moistened, 
and  allow  to  remain  some  time.  State  results. 

Invert  another  bottle  or  test-tube  filled  with  sulphur  dioxide,  over  a 
small  evaporating  dish  of  water.  Does  the  water  rise  in  the  tube? 
Why  ?  Test  the  water  with  blue  litmus  paper ;  what  effects  ?  What 
has  been  formed  with  the  water? 

16.  Characteristics  of  Sulphur  Dioxide.  —  It  is  a  very 
irritating,  colorless  gas,  considerably  heavier  than  air.  It 
is  soluble  in  water,  forming  an  acid  solution,  which,  how- 
ever, is  very  unstable.  It  will  neither  burn  nor  support 
combustion,  though  magnesium  ribbon  will  burn  in  it  with 
difficulty  as  it  does  in  carbon  dioxide.  It  is  readily  lique- 
fied by  passing  the  gas  through  a  spiral  tube,  surrounded 
by  ice  and  salt.  In  the  liquid  condition  it  is  limpid,  trans- 
parent, and  very  slightly  yellow  in  color. 
^  / 

' 


SULPHUR  AND  ITS  COMPOUNDS  179 

17.  Sulphur   dioxide   is  a  great   reducing  agent,  like 
carbon,  but  more  active.     That  is,  it  has  the  power  of 
abstracting  oxygen  from  other  substances.      If  sulphur 
dioxide  is  passed  into  a  bottle  containing  nitrogen  te- 
troxide,  NO2,  the  red  fumes  will  soon  disappear  because 
the  tetroxide  has  been  deprived  of  a  portion  of  its  oxygen 
and  converted  into  the  dioxide,  thus  :  — 

S02  +  N02  =  S03  +  NO. 

Likewise  a  current  of  sulphur  dioxide  passed  into  a 
solution  of  potassium  dichromate,  or  permanganate,  will 
deprive  them  of  a  portion  of  their  oxygen,  changing  the 
first  to  a  compound,  green  in  color,  and  rendering  the 
second  colorless.  It  will  be  important  to  remember  this 
property  on  account  of  its  relation  to  the  manufacture  of 
sulphuric  acid,  to  be  shown  later. 

18.  Uses  of  Sulphur  Dioxide.  —  These  have  already  been 
mentioned.      It  is  used  frequently  as  a  disinfectant  or 
fumigant,  and  for  bleaching  silk  and  straw  goods.     Evap- 
orated  fruits,  especially  apples  and  peaches,  owe   their 
white,  almost  natural,  color  to  the  bleaching  effects  of 
sulphur  dioxide,  which  is  allowed  to  flow  over  the  fruit 
as  it  is  put  into  the  evaporator.     Its  most  extensive  use  is 
for  making  sulphuric  acid. 

19.  Sulphur  Acids.  — Sulphur  forms  several  acids  with 
hydrogen  and  oxygen,  not  all  of  which  are  important. 
The  best  known  is  sulphuric,  H2SO4,  also  called  oil  of 
vitriol. 

EXPERIMENT  123.* —  Arrange  three  flasks  as  shown  in  Fig.  47,  one 
for  the  generation  of  sulphur  dioxide  by  the  treatment  of  copper  with 

*  If  it  is  found  necessary  to  use  simpler  apparatus,  fill  a  flask  with  sul- 
phur dioxide,  and  introduce  into  it  a  swab  of  cloth  upon  the  end  of  a  glass 
rod,  moistened  with  nitric  acid.  Soon,  brown  fumes  will  begin  to  appear, 


180 


MODERN  CHEMISTRY 


sulphuric  acid,  another  containing  nitric  acid  and  copper  turnings  f OT 
the  preparation  of  nitrogen  dioxide,  and  a  third  containing  water  to 
be  converted  into  steam.  Connect  with  a  large  flask,  Z>,  which  has 
a  fourth  tube  to  allow  the  entrance  of  air. 


t( 


FIG.  47. 

When  the  nitrogen  dioxide  enters  the  flask,  Z>,  containing  air,  it 
combines  with  the  oxygen,  forming  the  tetroxide,  thus :  — 

2  NO  +  O2  =  2  N02. 

Immediately  the  sulphur  dioxide  attacks  this  compound  of  nitrogen, 
taking  away  two  atoms,  reducing  it  to  the  dioxide  again,  thus :  — 

NO2  +  SO2  =  NO  +  SO3. 

The  dioxide  thus  formed,  with  the  oxygen  of  the  air,  again  combines 
to  form  the  tetroxide,  and  so  serves  as  a  carrier  of  oxygen  from  the 
air  to  the  sulphur  dioxide. 

Next,  the  sulphur  trioxide  combines  with  the  water  introduced  in 
the  form  of  steam,  producing  sulphuric  acid,  thus :  — 

SO3  +  H2O  =  H2SO4. 


showing  that  the  nitric  acid  is  being  decomposed  and  the  sulphur  dioxide 
converted  into  the  trioxide.  Now  add  a  few  cubic  centimeters  of  water, 
and  shake.  The  flask  will  contain  a  dilute  solution  of  sulphuric  acid. 


SULPHUR  AND  ITS  COMPOUNDS  181 

20.  To  test  the  Acid   prepared.  —  Put  a  little  of  the 
acid  into  a  test-tube  and  add  1  or  2  cc.  of  a  solution 
of  barium  chloride.     If  a  white  precipitate  forms,  which 
is  not  soluble  in  nitric  or  hydrochloric  acid,  or  both  to- 
gether, sulphuric  acid  is  indicated. 

21.  The  Manufacture  of  Sulphuric  Acid.  —  This  acid  is 
now  prepared  in  immense  quantities.     The  United  States 
and  Great  Britain  each  produce  annually  about  one  million 
tons,  and  Germany  is  not  far  behind.     Formerly,  sulphur 
was  used  to  prepare  the  sulphur  dioxide  for  the  manufac- 
ture of  this  acid,  but,  as  stated  above,  the  attempt  to  con- 
trol the  entire  output  of  the  Sicilian  mines  raised  the  price 
to  such  an  extent  that  sulphuric  acid  manufacturers  sought 
other  sources,  and  finally  discovered  the  present  method. 
The  pyrite  is  roasted  in  the  presence  of  plenty  of  air,  and 
the  following  reaction  takes  place  :  — 

2  FeS2  +  11  O  =  Fe2O3  +  4  SO2. 

22.  These  fumes  are  conducted  into   large   chambers 
lined  with  sheet  lead,  into  which  jets  of  steam  are  con- 
stantly sprayed,  together  with  nitric  acid  vapors,  obtained 
by   treating   sodium   nitrate   with   sulphuric   acid.     The 
reactions  that  take  place  in  these  lead  chambers  are  the 
same  as  already  described.     The  amount  of   nitric  acid 
necessary  is  very  small,  and  theoretically  might  be  used 
indefinitely,  but  practically  it  is  gradually  carried  by  the 
draughts  of  air  into  the  flues  and  must  be  replaced. 

The  sulphuric  acid  thus  prepared  collects  upon  the  floors 
of  the  rooms, — which  are  so  large  that  a  dancing  party 
of  a  hundred  couples  could  easily  be  held  in  them,  —  and 
is  called  chamber  acid.  It  is  only  moderately  strong,  and 
is  next  evaporated  in  leaden  vessels  until  a  specific  gravity 
of  a  little  over  1.7  is  reached,  when  it  begins  to  attack  the 


182  MODERN  CHEMISTRY 

lead.    It  is  next  concentrated  in  glass  or  platinum  retorts. 
(See  Fig.  48.)     The  following  simpler  plan  has  recently 


FIG.  48.  — Apparatus  for  condensing  Sulphuric  Acid. 

been  introduced.  Sulphur  dioxide  and  air  are  passed  over 
finely  divided  platinum  or  ferric  oxide,  whereby  sulphur 
trioxide  is  formed.  This  is  then  treated  with  water. 

23.  Characteristics  of  Sulphuric  Acid.  —  It  is  a  colorless, 
sirupy  liquid ;  it  received  the  name  oil  of  vitriol  on  this 
account,  and  because  it  was  made  horn  green  vitriol,  ferrous 
sulphate.     It  is  not  a  volatile  acid,  and,  unlike  nitric  or 
hydrochloric,  gives  off  no  odor.     It  is  very  heavy  and  very 
corrosive.     Organic  matter  exposed  to  it  is  charred  black, 
as  already  noticed.     It  has  great  affinity  for  water,  so 
much  so  that  a  beaker  two-thirds  filled  with  strong  acid 
will  in  a  few  weeks,  if  left  exposed  to  the  air,  absorb 
enough  moisture  to  cause  the  beaker  to  overflow.     Like- 
wise when  strong  acid  is  added  to  water,  or  vice  versa, 
the  mixture  becomes  very  hot,  reaching  nearly  100°  C., 
owing  to  the  strong  affinity  of  the  two  for  each  other. 

24.  It  is  upon  this  principle  that  sugar,  C12H22On,  is 
charred.     The  hydrogen  and  oxygen,  being  sufficient  to 
form  eleven  molecules  of  water,  are  abstracted,  and  the 
carbon  remains  behind  as  a  black  mass.     Upon  the  same 


SULPHUR  AND  ITS  COMPOUNDS  183 

principle  depends  its  use  as  a  drying  agent  for  various 
gases.  They  are  made  to  bubble  up  through  a  bottle  of 
strong  sulphuric  acid,  and  by  this  means  lose  their 
moisture. 

25.  Uses  for  Sulphuric  Acid.  —  It  will  be  concluded  from 
the  vast  quantities  manufactured  that  sulphuric  acid  is  a 
very  important  article  of  commerce.     It  is  the  most  useful 
of  acids,  and  almost  all  the  others  are  dependent  upon 
it   for   their  preparation.      In   the   manufacture  of  soda 
crystals,  Na2CO3,  by  the  Leblanc  process  (see  page  211), 
sulphuric  acid  is  indispensable.     This  salt,  Na2CO3,  is  the 
basis  for  all  soap  manufacture  as  well  as  for  glass,  baking 
powders,  etc.     We  can  thus  see  the  commercial  importance 
of  sulphuric  acid. 

26.  Another  very  extensive  use  is  in  the  manufacture 
of  artificial  fertilizers  from  bones.     When  they  have  had 
the  bone  oil  and  gelatine  removed,  and  as  bone-black  are 
no   longer  valuable   for  clarifying  sugar,  the   bones  are 
treated  with  sulphuric  acid.     This  converts  the  phosphates 
present  into  a  soluble  form  that  may  be  used  by  plants. 
Sulphuric  acid  is  also  used  in  the  manufacture  of  such 
explosives  as  nitroglycerine  and  gun-cotton,  for  making 
glucose,  and  in  some  of  the  processes  of  electroplating  and 
electrotyping. 

27.  Other  Acids  of  Sulphur.  —  Sulphurous  Acid,  H2S03.  — 
This  acid    has   already   been   mentioned,  as  well   as   its 
method  of  formation  and  its  instability. 

We  also  have 

Hyposulphurous,      H2SO2. 
Fuming  Sulphuric,  H2S2O7, 

which  is  really  ordinary  sulphuric  acid,  charged  with 
sulphur  trioxide,  SOg. 


1$4  MODERN  CHEMISTRY 

28.  Thiosulphuric  Acid,  H2S203.  —  This  last  is  of  some 
interest  because  it  is  the  basis  of  the  salts  known  as 
thiosulphates,  the  best  known  of  which  is  sodium  thiosul- 
phate,  Na2S2O3.  From  a  mistaken  idea  of  its  composition 
sodium  thiosulphate  was  first  named  hyposulphite,  and  is 
still  commonly  sold  under  that  name.  This  is  the  photog- 
rapher's "hypo." 

SUMMARY  OF  CHAPTER 

Sulphur  —  Where  found. 

Forms  in  which  it  occurs. 
Sources  of  commercial  supply. 
Methods  of  purification. 
Characteristics  of  sulphur. 

Various  forms  —  How  prepared. 

How  different. 
Uses  of  sulphur. 
Compounds. 

With  hydrogen  —  Two  names  for  the  gas. 
Occurrence. 
Method  of  preparing. 

Characteristics  of,  and  proof  by  experiment. 
Use  of. 

With  oxygen  • —  Names  and  formulae. 
Preparation  of  the  more  important. 
Comparison  of  method  with  that  of  making  hydrogen. 
Characteristics  of  SO2. 
Uses. 
With  hydrogen  and  oxygen. 

Most  important  —  Commercial  name. 

How    manufactured  —  Explanation    of    the    chemical 

changes  involved. 
Characteristics  of  H2SO4. 
Uses. 


CHAPTER  XIV 

SILICON  AND  ITS  COMPOUNDS  —  GLASS 
SILICON  :  Si  =  28 

1.  Abundance.  —  Silicon   is   never   found   free,  but   in 
the  form  of  compounds  is  one  of  the  most  widely  dis- 
tributed as  well  as  one  of   the   more   abundant   of   the 
non-metallic  elements.     Sand,  an  oxide  of  silicon,  SiO2,  is 
familiar  to  all ;  quartz,  crystallized  or  massive,  including 
the  agate,  amethyst,  opal,  and  other  stones,  is  another 
variety  of  the  same  substance.     All  soils  contain  it  to  a 
greater  or  less  extent,  and  it  is  taken  up  by  plants  and 
enters  into  their  structure.     Combined  with  sodium,  cal- 
cium, magnesium,  aluminum,  and  other  metals  it  forms 
silicates  which  are  very  abundant.     In  this  class  may  be 
placed  granite,  mica,  and  many  other  substances. 

2.  Character  of  Silicon.  —  Silicon  has  been  prepared  in 
such  limited  quantities  that  not  a  great  deal  is  known 
about  it.     It  occurs  in  three  forms,  the  amorphous  and 
the  crystallized  or  lustrous  being  the  two  most  impor- 
tant.    At   high   temperatures   it   combines   readily  with 
oxygen  or  with  carbon  dioxide,  forming  the  dioxide. 

COMPOUNDS  OF  SILICON 

3.  As    already   stated,   silica   or   silicon   dioxide,  SiO2, 
is   the   most   abundant   compound.      In   the   crystallized 
form    it    is    often    called    rock    crystal,    and    is    found 
in  hexagonal  prisms,  often  more  or  less  modified.     Owing 

185 


186  MODERN  CHEMISTRY 

to  the  presence  of  foreign  substances,  silica  often  assumes 
a  variety  of  colors,  and  is  known  as  rose  quartz,  smoky 
quartz,  etc.  It  is  very  hard,  being  seven  in  the  scale,  is 
brilliant,  highly  refractive  when  cut,  and  is  often  used  for 
ornaments  in  imitation  of  diamonds.  It  melts  at  about 
2000°  C.,  and  is  soluble  in  alkalies  as  well  as  in  hydro- 
fluoric acid. 

4.  It  is  from  the  fact  above  mentioned  that  siliceous 
incrustations  occur  about  many  geysers.     These  springs 
are  alkaline  in  character,  and  at  the  high   temperature 
present  beneath  the  surface  dissolve  considerable  quanti- 
ties of  silica;  when  the  water  becomes  cold  and  exposed 
to  the  action  of  the  air,  it  is  not  able  to  hold  the  silica, 
and  this  is  deposited  upon  any  bodies  on  which  the  water 
may  fall.     The  power  of  alkalies  to  dissolve  silica  may 
often  be  observed  in  the  laboratory,  where  bottles  contain- 
ing ammonia,  caustic  soda  and  potash,  sodium  carbomtte 
solutions,  etc.,  become  etched  or  rough  on  the  inside,  and 
the  glass  stoppers  so  tight  as  to  render  their  removal  an 
impossibility. 

5.  The   Silicates.  —  Theoretically,    silica   is   the    anhy- 
dride of  silicic  acid ;  that  is, 

Si02  +  2  H20  =  H4Si04. 

But  water  added  to  the  oxide  in  this  case  produces  no 
reaction.  The  silicates,  however,  are  based  upon  this  acid. 
They  are  abundant,  and  many  of  them  are  very  complicated 
in  composition.  As  silicic  acid  is  tetrabasic,  the  hydrogen 
may  be  replaced  by  a  variety  of  elements,  even  in  the 
same  molecule  ;  thus,  we  might  have 

NaAlSiO4:  Sodium  Aluminum  Silicate. 
CaMgSiO4:  Calcium  Magnesium  Silicate. 


SILICON  AND  ITS  COMPOUNDS — GLASS          187 

NaKCaSiO4  :  Sodium,  Potassium  Calcium  Silicate. 
H8Mg5Fe7Al2Si3O18 :  Mica,  etc. 

6.  Preparation  of  Silicic  Acid.  —  Silicic  acid  may  be  pre- 
pared from  "  water  glass,"  that  is,  silica  dissolved  in  boiling 
caustic  soda,  or  potash,  by  adding  a  little  strong  hydro- 
chloric acid  till  the  solution  is  no  longer  alkaline.     Then 
a  jellylike  mass  will  be  precipitated,  which  is  silicic  acid. 
By  filtering  this  out  and  igniting  when  dry  we  again 
obtain  the  oxide. 

EXPERIMENT  124.  —  Let  the  student  thus  prepare  some  soluble 
"  water  glass  "  and  the  silicic  acid  from  it. 

7.  Though  silica  is  insoluble  in  water  and  has  such  a 
high  melting  point  that  only  such  temperatures  as  that 
secured  by  the  oxy hydrogen  blowpipe  or  the  electric  fur- 
nace will  fuse  it,  still,  if  mixed  with  sodium  carbonate  and 
strongly  heated  in  a  blast  lamp  for  a  few  minutes,  it  is 
converted  into  a  soluble  form,  sodium  silicate,  and  may 
then  be  readily  taken  up  by  water. 

8.  Glass. — This  is  an  artificial  silicate  that  has  been 
manufactured  in  some  form  or  other  for  probably  4000 
years.     Several  of  the  nations  of  antiquity  were  famous 
for   their  wonderful   glasswork ;    in   beauty  of   coloring, 
their  achievements  have  probably  not  been  surpassed  in 
modern  times.     But  the  applications  of  glass  are  now  so 
varied  and  so  adapted  to  the  necessities  of  life,  as  well  as 
to  the  luxuries,  that  it  would  seem  impossible  to  do  with- 
out it.     Every  year  sees  the  manufacture  of  hundreds  of 
millions  of  bottles,  and  tons  of  other  kinds  of  glassware  ; 
and  the  art  of  glass  blowing  and  working  has  reached  such 
a  high  state  of  perfection  that  glass  objects,  from  their 
nature  almost  inconceivable,  are  now  of  frequent  manu- 
facture. 


188  MODERN  CHEMISTRY 

We  have  seen  above  that  if  silica  is  fused  with  sodium 
carbonate,  a  new  compound  is  formed  which  is  quite 
soluble.  If,  however,  we  mix  calcium  carbonate,  or  chalk, 
with  the  silica,  together  with  the  sodium  carbonate,  and 
fuse  the  mixture,  we  then  obtain  a  double  silicate  of 
sodium  and  calcium  that  is  quite  insoluble  in  water  and 
in  all  acids,  except  hydrofluoric. 

9.  Varieties  of  Glass. — There  are  many  varieties  of  glass. 
As  potassium  salts  are  so  closely  related  to  those  of  sodium, 
it  is  obvious  that  potash  could  be  used  instead  of  soda. 
In  fact,  glass  was  first  made  entirely  in  this  way.  Nearly 
all  the  best  chemical  and  physical  apparatus  is  still  made 
from  potash  salts,  and  this  variety  is  known  as  Bohemian 
glass.  It  is  much  harder  to  melt  than  glass  made  from 
sodium  carbonate. 

10.  If  an  oxide  of  lead  is  used  with  the  silica  and  potash, 
we  obtain  a  glass  that  is  very  soft  and  easily  worked, 
known  as  flint  glass.     It  has  a  very  high  refractive  power, 
and  on  this  account  is  used  for  telescopes  and  all  kinds  of 
optical  instruments.     In  the  purest  form  it  is  known  as 
strass  or  paste,  and  from  this  are  made  the  so-called  paste 
diamonds.      These  are  so  lustrous  and  highly  refractive 
that,  except  in  hardness,  it  is  difficult  for  any  but  experts 
to  distinguish  them  from  the  genuine  article. 

11.  Ordinary  glass,  known  as  crown  glass,  from  which 
windows  and  the  great  majority  of  glass  utensils  are  made, 
is  a  silicate  of  lime  and  sodium,  as  already  described. 
Ordinary  sand  contains  a  considerable   amount  of   iron 
in  the  form  of  an  oxide.     This  gives  to  the  glass  used 
for  ordinary  bottles  and  for  all  the  cheaper  grades  the 
well-known  greenish  color,  which,  however,  may  be  re- 
moved by  the  addition  of  a  small  quantity  of  manganese 
dioxide. 


SILICON  AND  ITS  COMPOUNDS — GLASS          189 

12.  Much  of  the  plain  glassware  used  at  present  is  molded 
just  as  any  casting  would  be  in  an  iron  foundry.     Window 
glass  is  first  blown  into  a  long  cylinder ;  this  is  cut  open 
and  flattened  while  still  hot  by  means  of  heavy  rollers. 
Plate  glass  for  large  windows  and  heavy  mirrors  is  cast. 
The  molten  glass  is  poured  upon  a  table  of  the  desired 
size,  allowed  to  cool,  and  the  surface  afterwards  ground 
and  polished. 

13.  All  glass  articles  must  be  carefully  annealed,  other- 
wise they  would  be  so  brittle  as  to  have  little  value.     The 
glass,  as  soon  as  shaped,  is  placed  in  an  oven,  and  during 
several  days  is  cooled  so  slowly  that  the  molecules  have 
time  to  adjust  themselves  to  stable  positions.     Indeed,  so 
well  is  this  annealing  done  that   glass  vessels  are  made 
for  use  in  chemical  work  that  may  be  heated  strongly  and 
plunged  into  cold  water  immediately  without  danger  of 
breaking. 

SUMMARY  OF  CHAPTER 

Silicon. 

Abundance  of  it  in  nature. 

Some  familiar  forms. 
Compounds  of  silicon. 

The  oxide  —  Some  common  forms. 

Characteristics  of. 
Glass  —  Importance  of. 

What  glass  is. 

Kinds  of  glass. 

How  different  in  properties. 

Making  of  window  glass  and  otker  forms. 

Annealing  of  glass  articles. 


CHAPTER  XV 

PHOSPHORUS  AND  ITS  COMPOUNDS 
PHOSPHORUS  :  P  =  31 

^  1.  Occurrence.  —  Phosphorus  has  been  known  for  about 
two  and  a  quarter  centuries,  but  it  is  only  since  1833  that 
it  has  had  any  real  practical  value.  Owing  to  its  strong 
affinity  for  oxygen  it  is  never  found  free,  but  in  the  form 
of  compounds  it  is  very  widely  distributed.  It  is  a  con- 
stituent of  many  rocks,  and,  from  their  decomposition,  also 
of  soils.  From  this  source  plants  take  it  up  and  store  it 
away  in  the  seeds  and  fruits ;  plants,  being  used  as  foods, 

transfer  it  to  animals,  where  it 
is  found  in  the  nerve  centers 
and  bones. 

Q^.  Manufacture  of  Phospho- 
rus. —  It  is  obtained  almost 
altogether  from  bones.  These 
are  put  into  retorts  and  heated, 
much  as  coal  is  for  the  prepa- 
ration of  illuminating  gas.  The 
volatile  products  are  thus  driven 
off  and  their  valuable  portions 
condensed.  The  bones  are  re- 
duced to  what  is  known  as 
bone-black,  or,  if  not  desired  for 
clarifying  sugar,  to  bone-ash. 
To  this  sulphuric  acid  is  added,  which  converts  the  cal- 
cium phosphate  in  the  bones  into  a  salt  that  is  soluble  in 

190 


FIG.  49.  —  Manufacture  of  Phos- 
phorus. 


PHOSPHORUS  AND  ITS  COMPOUNDS  191 

water.  This  is  dissolved  out  and  the  solution  evaporated 
to  dryness,  then  mixed  with  carbon  and  strongly  heated. 
The  phosphorus  is  thus  set  free ;  it  distills  out  and  is 
condensed  under  water  and  molded  into  sticks.  (See 
Fig.  49.)  R,  -R,  are  the  retorts  into'  which  the  mixture 
of  charcoal  and  phosphorus  compounds  are  put ;  F  is  the 
furnace,  and  TP,  IF,  the  water  tanks  where  the  phosphorus 
is  condensed.  The  process  is  very  deleterious  to  health, 
the  fumes  from  the  retorts  often  producing  dangerous 
ulcerations  of  the  jawbones,  a  disease  which  is  practically 
incurable. 

(3p  Characteristics  of  Phosphorus.  —  Phosphorus  is  a 
very  pale,  amber-colored,  translucent  solid,  somewhat  waxy 
in  appearance.  When  exposed  to  the  air  it  almost  imme- 
diately begins  to  give  off  luminous  fumes  having  a  faint 
garlic  odor,  and  in  the  course  of  a  short  time  takes  fire. 
A  little  friction  will  readily  ignite  it,  hence  it  should  be  cut 
under  water.  Burns  from  it  are  very  serious  and  require 
weeks  to  heal.  If  heated  to  240°  out  of  contact  with  the 
air,  it  changes  to  an  allotropic  form,  known  as  red  or 
amorphous  phosphorus.  Unlike  the  ordinary  phosphorus, 
this  is  not  poisonous,  does  not  readily  take  fire,  is  not  solu- 
ble in  carbon  disulphide,  and  does  not  glow  in  the  dark. 

EXPERIMENT  125.  —  To  show  the  ready  combustibility  of  phos- 
phorus when  finely  divided.  Dissolve  a  small  piece  of  phosphorus, 
half  as  large  as  a  pea,  in  a  little  carbon  disulphide.  Pour  the  solution 
upon  a  piece  of  filter  or  blotting  paper,  and  let  it  dry.  Notice  how 
quickly  it  ignites.  • 

EXPERIMENT  126.  —  To  show  that  phosphorus  will  burn  under 
water.  Put  into  a  small  bottle  about  1  g.  of  potassium  chlorate,  add 
a  few  small  pieces  of  phosphorus,  and  cover  with  water.  By  means  of 
a  pipette  or  funnel  tube  introduce  beneath  the  water  into  contact  with 
the  potassium  chlorate  a  little  sulphuric  acid.  Notice  that  the  phos- 
phorus begins  to  ^urn.  Explain. 


192  MODERN  CHEMISTRY 

EXPERIMENT  127.  —  To  show  the  affinity  of  phosphorus  for  chlo- 
rine, bromine,  and  iodine.  Put  a  small  piece  of  phosphorus  into  a 
deflagrating  spoon  and  introduce  it  into  a  jar  of  chlorine.  What 
happens  in  a  few  moments?  Cut  a  thin  slice  of  phosphorus,  and 
upon  it  place  a  crystal  of  iodine.  Notice  that  the  phosphoras  is  soon 
ignited.  Try  a  drop  of  bromine  in  the  same  way. 


Uses  for  Phosphorus.  —  About  3000  tons  of  phos- 
phorus are  manufactured  annually,  most  of  which  is  used 
in  preparing  matches.  Small  quantities  also  are  employed 
in  making  poisons.  Matches  were  first  made  in  Austria 
by  tipping  small  pine  sticks  with  sulphur  to  which  a  little 
phosphorus  had  been  added.  This  method  was  employed 
for  a  good  many  years,  but  the  sulphur  has  now  been 
largely  replaced  by  other  substances  rich  in  oxygen,  such  as 
potassium  chlorate,  saltpeter,  etc.,  together  with  paraffine. 

5.  Matches  are  now  made  entirely  by  machinery,  and 
with  wonderful  rapidity.     The   wood,  being  sawed  into 
convenient  lengths,  is  pressed  against  knives,  which  split 
it  up  into  the  proper  size  for  matches.     These  are  dipped 
into  paraffine,  then  tipped  with  a  paste  made  of  a  little 
glue    containing   phosphorus   and   the    other   ingredients 
already  mentioned,  toge^rkr  with  some  coloring  matter. 
After  drying  they  are  packed  in  boxes.       In   this  way 
a   single    machine  will   make    and   pack    several   million 
matches   in   a   day.     In  the  case  of   safety  matches  the 
phosphorus  is  placed  in  the  prepared  surface  upon  the 
box,  and  the  matches  can  be  ignited  only  by  friction  on 
this  surface. 

6.  Compounds  of  Phosphorus.  —  One  of  the  most  inter- 
esting of  these  is  hydrogen  phosphide,  PH3.     It  is  also 
called  phosphine  and  phosphoreted  hydrogen.     It  is  readily 
evolved  when  phosphorus  is  heated  in  a  solution  of  any 
strong  alkali,  such  as  caustic  soda  or  potash. 


PHOSPHORUS  AND  ITS  COMPOUNDS 


193 


FIG.  50. 


EXPERIMENT  128.  —  Suitable  for  class-room.  Into  a  small  flask  put 
about  50  cc.  of  strong  caustic  soda  or  potash  solution,  and  add  several 
small  pieces  of  phos- 
phorus. Pour  in  about 
a  cubic  centimeter  of 
ether,  and  close  the 
flask  quickly  with  a 
cork  and  long  delivery 
tube.  Support  the 
flask  upon  a  ring-stand, 
as- shown  in  the  figure, 
and  heat  moderately. 
Presently  smoky-look- 
ing fumes  will  fill  the 
flask,  and  then  the 
bubbles  issuing  from 
the  mouth  of  the  de- 
livery tube  will  take 
fire  spontaneously.  If 
the  room  is  free  from  draughts  of  air,  beautiful  rings  of  smoke,  grow- 
ing gradually  larger,  will  float  upward.  Notice  the  vortex  motion  of 
the  rings.  The  ether  is  introduced  to  expel  the  air  before  any  phos- 
phine  is  generated ;  the  heat  should  be  regulated  so  as  not  to  allow 
too  rapid  an  evolution  of  gas,  otherwise  the  rings  will  follow  in  such 
rapid  succession  as  to  break  one  another.  What  is  the  odor  of  the 
gas?  Color? 

7.  Oxides  of  Phosphorus. — Pentoxide,  P205,  and  Tri- 
oxide,  P203.  The  first  of  these  has  been  seen  on  various 
occasions :  when  phosphorus  was  burned  in  oxygen,  in 
preparing  nitrogen,  etc.  The  dense  white  fumes  noticed 
consisted  mainly  of  phosphorus  pent  oxide.  This  com- 
pound is  always  obtained  when  phosphorus  is  burned  in  a 
plentiful  supply  of  oxygen.  When  the  amount  is  limited, 
or  when  the  combustion  is  slow,  phosphorus  trioxide  is 
obtained.  The  peiitoxide  is  a  white  solid  which  has  great 
affinity  for  moisture,  and  if  dropped  into  water  combines 
with  it  with  a  hissing  sound  as  of  a  hot  iron  in  cold  water. 


194  MODERN  CHEMISTRY 

8.  Acids  of  Phosphorus.  —  The  two  oxides  named  above, 
like  the  corresponding  oxides  of  nitrogen,  are  the  anhy- 
drides of  certain  acids,  thus  :  — 

P2O3  +  3  H2O  =  2  H3PO3    .     .     .     Phosphorous  Acid 
P2O5  +  3  H2O  ==  2  H3P04    .     .     .     Phosphoric      " 

The  latter  is  the  more  important.  It  will  be  noticed  th tit- 
its  molecule  contains  three  atoms  of  hydrogen,  all  of  which 
may  be  replaced  by  a  metal.  Such  acids  are  called  tribasic. 
Phosphoric  acid  is  a  white  crystalline  substance,  which 
may  be  prepared  by  treating  bone-ash  with  sulphuric  acid. 
At  high  temperatures  it  will  give  up  a  part  of  the  water 
that  was  taken  in  its  formation  and  yield  metaphosphoric 
acid,  HPO3,  which  is  monobasic.  The  reaction  may  be 
shown  thus :  — 

H8PO4  +  heat  =  HPO3  +  H2O. 

This  is  frequently  sold  under  the  name  glacial  phosphoric 
acid. 

9.  Compounds  with  Phosphoric  Acid.  Phosphates. — The 
most  common  of  these  is  calcium  phosphate,  Ca3(PO4)2, 
found  in  the  bones.  Immense  deposits  of  this  are  found 
in  Florida,  where  it  is  mined  and  used  as  a  fertilizer  in 
various  parts  of  the  world.  From  the  fact  that  all  grain 
plants  absorb  the  soluble  phosphates  from  the  soils,  unless 
these  salts  are  replaced  in  some  way  the  land  rapidly  loses 
its  productive  power.  A  considerable  portion  of  the  phos- 
phates in  the  grain  fed  to  animals  is  thrown  off  in  the  ex- 
crement and  is  returned  to  the  soil  in  this  way. 

10.  Immense  quantities  of  bones  are  reduced  to  animal 
charcoal,  and  then,  by  treatment  with  sulphuric  acid,  con- 
verted into  soluble  phosphates  and  returned  to  the  soil 


PHOSPHORUS  AND  ITS  COMPOUNDS  195 

in  this  way  as  artificial  fertilizers.  Another  source  of 
considerable  supply  is  from  the  reduction  of  phosphorus- 
bearing  iron  ores  by  the  Thomas- Gilchrist  process  ;  and  'a 
matter  of  interest  in  this  connection  is  that  the  calcium 
phosphate  thus  obtained  is  already  in  the  soluble  form  and 
needs  no  further  treatment. 


SUMMARY  OF   CHAPTER 

Phosphorus  —  Occurrence. 
Source  of  supply. 
Method  of  preparing  phosphorus. 

By-products  and  their  uses. 
Characteristics. 

Two  forms  of  phosphorus. 

Compare  with  forms  of  sulphur. 
Experiments  to  illustrate  characteristics. 
Uses. 

Method  of  making  matches. 
Chemicals  used. 
Compounds. 

With  hydrogen. 

How  prepared. 
With  oxygen. 

Names  and  formulae. 
How  prepared. 
WTith  hydrogen  and  oxygen. 
How  related  to  the  oxides. 
Salts  formed  from  these  acida. 
Uses. 


CHAPTER   XVI 
AVOGADRO'S  LAW  — ATOMIC   WEIGHTS  —  PROBLEMS 

1.  Avogadro's  Law.  — This  law,  or  hypothesis,  was  for- 
mulated by  the  Italian  physicist  and  chemist,  Avogadro, 
and  afterward,  independently,  by  the  Frenchman,  Ampere. 
It  may  be  stated  thus  :  - 

r^>  Equal  volumes  of  all  substances  in  the  gaseous  condition 
f_fj  under  the  same  pressure  and  temperature  contain  the  same 
number  of  molecules.  To  illustrate,  suppose  a  liter  of 
hydrochloric  acid  gas  contains  a  billion  molecules,  then 
a  liter  of  nitrous  oxide,  or  of  any  other  gas,  would  also 
contain  a  billion  molecules. 

2.  Proof  of  this  Theory.  —  No  absolute  proof  of  this 
law  has  ever  been  given,  but  many  facts  seem  to  favor 
such  a  theory.     For  example,  we  have  seen  that  all  gases 
expand  and  contract  in  the  same  ratio  under  the  influence 
of  heat  and  pressure.     As  expansion  and  contraction  mean 
simply  a  change  in  the  distance  which  separates  the  mole- 
cules from  each  other,  this  being  greater  when  the  body 
is  heated,  and  less  when  cooled,. it  would  seem  that  bodies 
could  expand  alike  only  if  composed  of  the  same  number 
of  molecules,  or  if  containing  what  means  the  same  thing, 
the  same  number  of  intermolecular  spaces. 

3.  Ratio  of  Molecular  Weight  to  Specific  Gravity.  —  It 
\    has  been  found  also  that  there  is  a  constant  ratio  existing 

between  the  molecular  weight  of  a  gaseous  body  and  its 
specific  gravity  ;  that  is,  if  we  divide  the  molecular  weight 
of  any  gas  by  its  specific  gravity,  we  always  obtain  prac- 

196 


ATOMIC  WEIGHTS  197 

tically  the  same  quotient.  This  ratio  is  about  28.88. 
Thus,  the  molecular  weight  of  carbon  dioxide  is  44,  its 
specific  gravity  is  1.524,  the  ratio  of  44  to  1.524  is  28.87 ; 
carbon  monoxide  has  a  molecular  weight  of  28,  specific 
gravity  of  0.967,  the  ratio  is  28.94. 

EXERCISE.  —  To  apply  this  fact,  suppose  a  given  volume  of  nitrous 
oxide,  X2O,  weighs  1.52  grams,  and  the  same  volume  of  hydrochloric 
acid  gas  weighs  1.27  grams.  It  is  evident  that  the  weight  of  any 
volume  of  gas  divided  by  the  weight  of  one  molecule  would  give  the 
number  of  molecules  in  that  volume.  Thus  :  — 

wt.  of  1 1.  x.,o  =  no  mol  N  o  in  l  uter 

wt.  of  1  mol. 

nd  -       wt.  of  1  1.  HC1 

wt.  of  1  mol.  HC1 

We  can  readily  find  the  weight  of  a  liter  of  each  of  these  gases, 
and  also  the  molecular  weight  of  each,  but  the  first  is  in  grams  and  the 
second  in  microcriths,  that  is,  so  many  times  as  heavy  as  a  hydrogen 
atom ;  but  unfortunately  we  have  no  means  of  knowing  how  many 
microcriths  in  a  gram,  hence  we  cannot  perform  the  division  indicated 
above  nor  assign  to  the  quotient  any  concrete  name.  If  we  make 
the  division,  however,  we  find  that  the  quotient  is  always  practically 
the  same ;  that  is, 

wt.  of  1  vol.  N2O 
wt.  of  1  mol.  X2O 

**•  °f  *  V°|-  *TC1  =  28.83  =  no<  moh  HC1  in  !  voL 
wt.  of  1  mol.  HC1 

Hence,  as  the  ratio  in  each  case  is  the  same,  in  accordance  with  the 
axioms  of  geometry, 

no.  mol.  N2O  in  1  vol.  =  no.  mol.  HC1  in  1  vol. 
Putting  this  law  into  the  form  of  a  proportion,  it  would  read :  — 

mw      m  w  i   ,  , 

= ,  or  mw  :  m'w'  '.'.sis'. 

s          s' 

in  which  mw  and  m'w1  represent  the  molecular  weights  of  any  two 
gases,  and  s  and  s'  their  specific  gravities. 


198  MODERN  CHEMISTRY 

4.  Application  of  this  Law.  —  The  truth  of  Avogadro's 
Law  having  been  accepted  long  ago,  it  is  now  made  use  of 
in  determining  the  molecular  weights  of  new  compounds. 
Having  found  lay  actual  work  the  weight  of  1  liter  of  the 
gas,  and  knowing  the  weight  of  1  liter  of  air,  the  specific 
gravity  is  found.     Then,  substituting  in  the  formula, 

™?=  28.88, 

S 

we  can  easily  find  the  value  of  mw. 

5.  Finding  Atomic  Weights.  —  This  law  is  further  used 
in  determining  the  atomic  weight  of  a  newly  discovered 
element. 

Let  m  represent  this  element,  and  suppose  we  are  attempting  to 
find  the  atomic  weight  by  studying  some  compound  of  it  with  oxygen. 
We  should  find  the  weight  of  a  molecule  of  the  oxide  as  shown  above. 
Suppose  this  is  found  to  be  28.  Next,  by  chemical  analysis  we  should 
determine  what  per  cent  of  the  compound  is  the  new  element,  m. 
Suppose  the  analysis  shows  this  to  be  42.86  per  cent,  then  we  should 
have  this  proportion:  — 

mol.  wt. :  wt.  of  m  in  the  mol. : :  100  per  cent :  per  cent  of  m; 
or,  28  :  x  : :  100  :  42.86. 

100  x  =  42.86  x  28. 
x  =12. 

In  the  same  way  we  should  determine  the  weight  of  the  element,  m, 
in  a  molecule  of  a  number  of  other  compounds  containing  it ;  then, 
the  one  having  the  least  amount  would  be  taken  as  a  compound  con- 
taining but  one  atom  of  the  element,  and  the  value  of  x  in  that  com- 
pound would  represent  the  atomic  weight.  To  illustrate,  suppose  in 
this  way  we  find  in  our  analyses,  and  subsequent  determinations,  that 
moi -  x  is  equal  to  24,  12,  36,  120.  The  second,  12,  being  the  smallest 
amount  found  in  any  compound,  would  be  accepted  as  the  atomic 
weight.  This  would  not  be  absolute  proof,  however,  as  later  another 
compound  might  be  discovered  which  contained  a  smaller  amount  of 
m,  in  which  case  that  smaller  amount  would  be  taken  as  the  atomic 
weight. 


ATOMIC   WEIGHTS 


199 


6.    Constitution  of  the  Molecules  of  Elements.  —  How 

many  atoms  are  there  in  a  molecule  of  an  elementary  sub- 
stance, like  oxygen,  hydrogen,  etc.  ?  In  writing  some  of 
the  reactions  in  the  earlier  part  of  this  book  the  molecules 
were  shown  as  having  two  atoms.  With  some  exceptions, 
this  is  true ;  that  is,  a  molecule  of  hydrogen,  oxygen, 
chlorine,  and  of  many  other  elements  contains  two  atoms. 
How  do  we  know  this?  A  proof  in  the  case  of  one  or 
two  elements  will  illustrate  for  the  others. 

We  have  seen  that  when  hydrogen  and  chlorine  are  caused  to  unite, 
they  form  hydrochloric  acid.  It  is  found  also  by  further  experiment 
that  in  uniting  thus  the  volume  is  not  decreased ;  that  is,  if  we  put 
together  a  liter  of  chlorine  and  one  of  hydrogen,  after  causing  them 
to  combine,  we  have  2  liters  of  hydrochloric  acid.  Perhaps  it  will  be 
clearer,  stated  in  the  form  of  an  equation,  thus :  — 

1000  cc.  of  Cl  +  1000  cc.  of  H  =  2000  cc.  of  HC1. 

Now,  according  to  Avogadro's  Law,  there  would  be  the  same  number 
of  molecules  in  a  liter  of  chlorine  as  of  hydrogen  or  of  hydrochloric 
acid.  Dividing  the  entire  equation  through  by  this  common  factor, 
the  number  of  molecules  of  chlorine  in  1  liter,  or  1000  cc.,  we  should 
have 

1  mol.  of  Cl.  +  1  mol.  of  H  =  2  mol.  of  HC1. 


Two  Molecules. 


Chemical  analysis  shows  that  in  hydrochloric  acid  the  hydrogen  and 
chlorine  are  united  in  the  ratio  of  1  to  35.5,  or  one  atom  of  each, 
as  represented  by  the  formula  HC1,  or  by  the  figure. 


200  MODERN  CHEMISTRY 

It  is  evident,  therefore,  that  two  molecules  of  hydrochloric  acid 
contain  two  atoms  of  hydrogen  and  two  of  chlorine,  and  as  we  only 
had  one  molecule  of  each  of  these  elementary  gases,  each  of  those 
molecules  must  have  contained  two  atoms.  In  a  similar  way  we 
would  prove  for  bromine,  fluorine,  oxygen,  and  others. 

7.  Most  Molecules  Diatomic.  —  Such  molecules  as  these 
are  called  diatomic.     There  are  a  few,  sodium,  potassium, 
cadmium,   mercury,  and   zinc,    whose   molecules   contain 
only  one  atom,  and  such  are  called  monatomic.      Their 
molecule  is,  therefore,  identical  with  the  atom.     Only  one 
triatomic  elementary  molecule  is  known,  and  that  is  the 
allotropic  form,  ozone.    A  few,  like  phosphorus  and  arsenic, 
are  tetratomic ;  that  is,  the  molecule  is  made  up  of  four 
atoms. 

8.  Application  of  this  Fact.  —  It  often  becomes  necos- 
sary  in  chemical  problems  to  know  the  weight  of  a  liter 
of  a  gas.     This  may  very  easily  be  found,  but  we  must 
first  know  its  vapor  density;  that  is,  its  density  compared 
to  hydrogen.      With   the  elementary  substances  this  is, 
as  a  rule,  the  same  as  the  atomic  weight ;  for  example, 
the  atomic  weight  of  hydrogen  is  1,  the  molecular  weight 
is  2 ;  the  atomic  weight  of  nitrogen  is  14  ;  the  molecular 
weight  28.     Hence,  whether  we  take  the  atomic  weight  of 
nitrogen,  or  its  molecular  weight  and  divide  by  the  molec- 
ular weight   of   hydrogen,    we   obtain   the   same  results. 
Then,  as  the  hydrogen  molecule  weighs  two,  we  find  the 
vapor   density  of   any  other   substance   by   dividing   its 
molecular  weight  by  2.     Thus  :  — 

1  mol.  N2O       weighs  2  x  14  +  16  =  44 

1"H  "        2x1  =  2 

1    "      N2O  "        44-7-2  times  as  much  as  1  mol.  H 


ATOMIC   WEIGHTS  201 

Again,  — 

1  mol.  CO  weighs  12  4- 16  =  28 

1"H  «          2x1=2 

1    "      CO  "        28  -T-  2  times  as  much  as  1  mol.  H 

Therefore,  vapor  density  ofCOis28-f-2=  14. 

Thus  find  the  vapor  density  of  CO2,  N2O3,  O,  HC1,  SO2, 
C1,N.  ^  jt  $  !*T  ^ 

\V*  9^  To  find  Weight  of  One  Liter  of  Any  Gas.  —  Having 
found  the  weight  of   a  gas  compared  to  hydrogen   (its 
vapor  density),  it  is  only  necessary  to  multiply  the  weight 
of  1  liter  of  hydrogen  by  this  figure.     A  liter  of  hydro-  -3 
gen  has  been  found  to  weigh  .0896  g.,  a  number  which    '- 
should  be  remembered.    Suppose  now  we  desire  to  find  the   ' , 
weight  of  a  liter  of  carbon  monoxide,  CO.     Above  we 
found  its  vapor  density  to  be  14.      Then,  as  a  liter  of  <* 
hydrogen  weighs  .0896  g.,  one  of  carbon  monoxide  will      /, 
weigh  14  x  .0896,  or  1.2544.  J, 

Thus  find  the  weight  of  1  liter  of  the  gases  whose  densi- 
ties were  found  above.  Also  of  N2O,  NH3,  H2S. 
rw  10.  The  Formulae  of  Compound  Bodies.  —  We  have 
learned  that  the  formula  of  a  compound  is  a  short  method 
of  expressing  its  composition.  It  may  be  of  interest  to 
know  how  to  determine  the  formula  of  a  compound.  The 
substance  is  first  carefully  analyzed,  and  the  percentage 
composition  determined. 

Suppose  \ve  have  in  mind  a  compound  which  analysis  shows  con- 
sists of  carbon  and  oxygen,  27.27  per  cent  of  the  former,  and  72.73  per 
cent  of  the  latter.  We  should  next  weigh  a  liter  of  it ;  suppose  we 
find  this  to  be  1.9712  g.  As  a  liter  of  hydrogen  weighs  .0896  g.,  the 
unknown  gas  is  1.9712  H-  .0896,  or  22  times  as  heavy. 

We  have  seen  that  the  molecular  weight  is  twice  the  vapor  density, 
then  the  weight  of  the  molecule  would  be  2  x  22,  or  44.  Now,  as  the 


202  MODERN  CHEMISTRY 

carbon  is  27.27  per  cent  of  this,  it  equals  .2727  of  44  =  11.9988,  and  the 
oxygen,  72.73  per  cent,  or  its  weight  in  the  molecule  is  72.73  per  cent  of 
44  =  32  +  .  Previous  experiments  have  shown  that  the  atomic  weight 
of  carbon  is  12,  hence  the  weight  found  above,  11.9988,  practically 
corresponds  to  one  atom,  and  that  would  be  the  amount  of  carbon  in 
the  compound.  In  the  same  way  as  the  atomic  weight  of  oxygen  is 
known  to  be  16,  the  amount  found  in  the  compound,  32,  would  indi- 
cate two  atoms.  The  substance  in  question,  therefore,  would  contain 
carbon,  1  atom,  oxygen,  2  atoms,  and  would  be  carbon  dioxide,  for- 
mula CO2. 

PROBLEMS.  —  1.    A  liter  of  a  certain  gas  weighs  0.8064.    It  consists 
of  hydrogen  £  and  oxygen  f .    Find  its  vapor  density,  molecular  weight, 
r<         and  the  formula. 

2.  A  gas  consisting  of  carbon  and  oxygen  has  42.86  —  per  cent  of 
\5  the  former,  and  57.14  +  per  cent  of  the  latter.     If  1  liter  of  it  weighs 

Qj      1.2544,  what  is  its  formula? 

3.  What  per  cent  of  turpentine,  C10H16,  is  carbon?     Hydrogen? 

4.  The  vapor  density  of  a  body  is  found  to  be  50.5.     If  analysis 
shows  that  2.359  g.  of  it  contain  1.12  g.  of  oxygen,  how  many  atoms 

p "'  of  oxygen  are  there  in  the  formula  representing  the  substance? 

5.  What  is  the  molecular  weight  of  a  certain  substance  if  50  g. 
of  it  contain  32.65  g.  of  oxygen,  knowing  that  there  are  four  atoms  of 
oxygen  in  the  molecule  of  the  substance? 

6.  Find  the  percentage  composition  of  nitric  acid. 


SUMMARY   OF   CHAPTER 

Avogadro's  Law  —  Statement  of  the  law. 
Illustration. 
Proof  of  the  law. 

a.  As  seen  in  effects  of  heat. 

b.  Ratio  of  molecular  weight  to  specific  gravity. 
Value  of  the  law. 

a.  Finding  atomic  weights  —  Illustration. 

b.  Constitution  of  molecules  —  Proof. 
Meaning  of  terms  monatomic,  etc. 

Problems. 

Method  of  finding  weight  of  a  liter  of  any  gas. 
How  to  determine  the  formula  of  a  compound. 


CHAPTER   XVII 


THE  METALS  — PERIODIC  LAW 

1.  Metals  and  Non-metals. — It  has  been  customary  to 
divide-  the  elements  into  two  great  classes,  the  metals  and 
non-metals,  of  which  the  former  includes  by  far  the  greater 
.  number.  This  classification,  however,  is  based  largely 
upon  the  external  characteristics  or  appearance  rather 
than  upon  the  chemical  deportment.  In  appearance  the 
metals  have  a  peculiar  luster,  known  as  the  metallic  luster, 
considerable  density,  with  few  exceptions  have  high  melt- 
ing points,  and  are  electro-positive  in  character.  As  A« 
rule,  their  oxides  are  not  anhydrides,  and  yet  there  ^re 
many  exceptions  to  this  statement,  for  we  find  various 
compounds  of  tin,  arsenic,  antimony,  chromium,  aluminum, 
etc.,  in  which  these  metals  seem  to  serve  as  the  acid-form- 
ing element.  And  some  even  possess  more  chemical  char- 


SON-METALS 


METALS 


Their  oxides,  with  water,  form 
acids,  as  for  example : 


S02      ...    H2S03, 
P2O5     .    .     .     HPO3,  etc. 

Many  are  gaseous. 
Many  are  transparent. 
Poor  conductors    of    heat   and 
electricity. 


Their  oxides,  with  water,  form 
bases,  as: 

CaO     .     .     .     Ca(OH)2, 
Na20    .     .    .     NaOIL 
K2O      .     .     .     KOH,  etc. 

Most  are  solids. 
All  are  opaque. 

Good  conductors   of  heat  and 
electricity. 


203 


204 


MODERN  CHEMISTRY 


acteristics  in  common  with  the  non-metals  than  with  the 
metals.  It  must  be  concluded,  therefore,  that  there  is  no 
clearly  dividing  line  between  the  two  classes.  Neverthe- 
less, some  distinctions  in  addition  to  those  mentioned 
above  may  be  noted. 

2.  Tabular  Classification. — It  will  be  seen  that  the 
above  division  is  almost  purely  an  arbitrary  one.  At  the 
present  time  it  is  customary  to  classify  the  elements  into  a 
number  of  groups  in  accord  with  what  is  known  as  the 
periodic  law. 

TABLE  OF  ELEMENTS 


I 

II 

III 

IV 

V 

VI 

VII 

VIII 

Period       I 

H  =  l 
Li  =  7 

Gl=9 

B  =  ll 

Coll 

N  =  14 

O=16 

F=19 

"         II 

Na-  -tf 

Mg'^1 

!      AL' 

tf  Si 

P 

8 

Cl 

Fe,  Co,  *  5  b 

yO     Ni 
f                   i. 

"        III  < 

K 

fec£ 

Scf 
Ga 

7^  ^e 

VAs 

Cri 

•     Se 

Mn 
Br 

"    ™{t 

Rb 

f     /Ag 

Sr'"" 

Y    : 

-  In 

%n 

Cb 

Mo  '- 

I 

Ru,  Rh,'  ] 
Pd 

"          V-f^ 

Cs*/ 

Ba  • 

La''' 

^Ce 

*  } 

"      VI(B 

Au 

Hg 

Yb 

Tl 

Pb 

Bi 

W 

Os,  Ir, 
Pt 

"    ™{* 

Th 

U"  V\ 

3.  Recurrent  Characteristics  in  the  Table.  —  If  the  above 
table  is  studied  in  connection  with  the  atomic  weights  of 
the  elements,  it  will  be  seen  that,  reading  from  left  to  right, 


THE  METALS  —  PERIODIC  LAW  205 

they  are  arranged  with  reference  to  their  weights.     Thus, 
in  the  first  period,  we  have 

Li  =  7,  Gl  =  9,  B  =  11,  C  =  12,  N  =  14,  O  =  16,  F  =  19 ; 

in  the  second, 

Na  =  23,  Mg=24,  Al=27,  Si=28,  P  =  31,  S=32, 01=35.5. 

4.  In  thus  arranging  them  it  was  noticed  that,  starting 
with  lithium,  not  until  we  reach  the  eighth  element  beyond, 
do  we  come  to  another,  sodium,  similar  to  lithium  in  char- 
acteristics ;  and  from  sodium  there  are  seven  more  before 
another  is  reached  similar  to  this.  From  these  observa- 
tions the  above  table  was  arranged,  and  though  it  is  far 
from  complete,  wonderful  results  have  come  from  it.  We 
notice  that  in  group  VII,  we  have  fluorine,  chlorine, 
bromine,  and  iodine,  four  elements  that  we  have  found 
to  have  very  similar  properties.  We  shall  hereafter  find 
the  same  to  be  true  of  lithium,  sodium,  and  potassium 
of  the  first  group ;  magnesium,  calcium,  strontium,  and 
barium  of  the  second,  and  so  on.  If  we  take  these  vertical 
columns  or  groups  and  compare  their  atomic  weights,  we 
notice  some  interesting  facts. 

*         2o  |  The  atomic  weight  of  sodium  is  exactly 
halfway  between  the  other  two. 


Ca=  40 
Sr  =  87 
Ba  =  136 

P    =    31 

As=  75 
Sb  =  120 


The  weight  of  strontium  is  practically 
the  mean  of  the  other  two. 


The  same  is  true  of  the  middle  element. 


206  MODERN  CHEMISTRY 

S    =    32' 

Se  =    79    The  same  is  true  of  the  middle  element. 

Te  =  125 . 

5.  If  we  study  the  compounds  that  the  elements  form, 
we  shall  find  that  those  falling  in  the  same  group  are 
strikingly   similar    in    their    chemical    behavior.     Thus, 
lithium,  sodium,  potassium,  rubidium,  and  caesium  in  the 
first  group  are  all  univalent  and  form  oxides  with  the 
general  formula,  M2O,  in  which  M  represents  any  metal 
of  the  group.     Furthermore,   they  form  no   compounds 
with  hydrogen.     If  we  take  the  second  group,  they  are 
all  bivalent,  forming  oxides  with   the   general  formula, 
MO,  as  MgO,  CaO,  etc.     They  form  no  hydrogen  com- 
pounds.    The  members  of  the  third  group  are  trivalent, 
as  seen  in  their  oxides,   A12O3,  general  formula  M2O3. 
And  so  we  might  go  on  through  the  table. 

6.  Vacancies  in  the  Table.  —  It  will  be  noticed  that  there 
are  many  vacant  places,  but  it  is  an  interesting  fact  that 
when  the  table  was  first  worked  out  there  were  many 
others  that  have  since  been  filled.     And  strange  to  say, 
from  this  table  the  author  of  the  plan  not  only  predicted 
that  these  very  elements  would  be  found,  but  even  gave 
in  a  general  way  their  characteristics,  and  in  accordance 
therewith  suggested  names  for  them.     In  the  same  way, 
it  is  possible  that  many  of   the  places   now  vacant  will 
sometime  be  filled  by  elements  as  yet  undiscovered. 

NOTE.  —  Some  teachers  may  prefer  to  defer  a  close  study  of  the  Periodic  Law  until  after 
the  completion  of  the  work  with  metals. 

SUMMARY  OF  CHAPTER 

Classes  of  the  elements. 
Characteristics  of  the  two  classes, 

Wherein  different. 

Wherein  alike. 


THE  ALKALI  METALS  207 

The  Periodic  Law. 

Recurrence  of  certain  characteristics. 
Relation  of  atomic  weights. 
Similarity  of  chemical  behavior. 
Value  of  the  law  and  table. 


CHAPTER   XVIII 

THE  ALKALI  METALS 

SODIUM:  NA  =  23 

1.  Its  Discovery. — Up  to  the  year  1807  caustic  soda 
and  caustic  potash  had  been  regarded  as  elementary  sub- 
stances ;    by  electrolysis,  however,  Sir  Humphry  Davy  in 
1807  proved  both  of  these  substances  to  be  compounds, 
and  hydroxides  of  the  metals  sodium  and  potassium. 

2.  Where  found.  —  Sodium  is  very  widely  distributed, 
traces  of  it  being  found  everywhere.     On  account  of  the 
strong  affinity  existing  between  it  and  water,   it  never 
occurs   in   the  metallic   state.     Its  most  abundant  com- 
pound is  common  salt,  NaCl,  which  constitutes  a  large 
per   cent   of   the   solid  matter  found  in  sea  water,  salt 
lakes,  and  springs ;  vast  deposits  of  it,  more  or  less  pure, 
occur   in   many   parts  of  the   West  as  well  as  in  other 
portions  of  the  world.     Sodium  nitrate,  NaNO3,  is  found 
in  immense  quantities  in  Chile  and  elsewhere.     Other  com- 
pounds occur  in  smaller  proportions,  but  in  some  form  or 
other  sodium  can  be  detected  in  the  particles  of  dust  that 
may  be  seen  floating  in  the  sunbeams. 

3.  Reduction  of  Sodium  from  its  Compounds.  —  Since 
the  isolation  of  the  metal  by  Davy,  various  other  plans 
have   been  tried,  but  they  are   all   modifications  of  the 


208  MODERN  CHEMISTRY 

original.     What  is  known  as  the  Castner  process  is  the 
one  generally  used  at  present.     See  Figure  51. 

A  in  the  figure  is  a  large  iron 
vessel,  B  another,  similar  but 
smaller,  inverted  over  A  and 
dipping  into  the  fused  caustic 
soda  in  the  lower  vessel.  It  is 
held  in  position  by  insulated 
supports  not  shown.  Through 
the  bottom  at  D  is  inserted  the 
negative  electrode,  and  B  serves 
as  the  positive.  When  the  cur- 
rent from  the  dynamo  is  passed  through,  the  caustic  soda 
is  electrolyzed,  B  gradually  fills  with  hydrogen  which 
bubbles  out  underneath,  while  the  metallic  sodium  col- 
lects upon  the  surface  of  the  fused  mass.  In  this  way 
it  is  prepared  for  about  two  dollars  a  pound. 

4.  Characteristics  of  Sodium.  —  It   is  a  silvery  white 
metal,  so  soft  at  ordinary  temperatures  that  it  may  be 
molded   with    the    fingers,  about    like    stiff    putty.      At 
—  20°  C.,  however,  it  becomes  hard.    It  tarnishes  so  rapidly 
in  the  air  that  only  for  an  instant  after  being  cut  can  its 
true  color  be  seen.     It  takes  up  moisture  and  carbon  di- 
oxide from  the  air,  forming  first  caustic  soda,  and  after- 
ward sodium  carbonate.     In  course  of  time  a  piece  of 
sodium  left  more  or  less  exposed  is  entirely  converted  into 
amorphous  sodium  carbonate.     It  is  usually  preserved  in 
naphtha  or  some  similar  light  oil  containing  no  oxygen. 

5.  Sodium  is  soluble  in  liquid  ammonia  and  forms  with 
it  a  blue  solution.     Its  properties  are  strongly  alkaline. 
If  heated  and  plunged  into  a  jar  of  chlorine  it  burns  vigor- 
ously, forming  common  salt.      Thrown  upon  water  it  is 
immediately  melted,  owing  to  the  heat  generated  by  the 


.     THE  ALKALI  METALS  209 

strong  chemical  action,  and  the  water  is  decomposed,  as 
already  shown  in  our  study  of  hydrogen.  If  a  burning 
match  is  touched  to. the  sodium  as  it  spins  about  on  the 
water,  the  hydrogen  will  burn  with  a  yellow  flame,  due  to 
the  vaporization  of  a  small  portion  of  the  sodium.  Upon 
moderately  warm  water  the  gas  will  take  fire  spontane- 
ously. If  a  small  piece  of  sodium  is  dropped  upon  a 
moistened  blotting  paper,  it  is  quickly  ignited.  If,  when 
it  begins  to  burn,  the  molten  sodium  is  allowed  to  roll  off 
and  drop  upon  the  floor,  it  will  burst  into  many  particles 
which  will  spin  about,  burning  with  the  characteristic  yel- 
low flame. 

EXPERIMENT  129.  —  Moisten  a  piece  of  blotting  paper  with  water, 
to  which  a  little  phenolphthalein  has  been  added.  Drop  a  small 
piece  of  sodium  upon  the  blotter.  Notice  the  red  track  it  leaves  as  it 
slowly  moves  about  from  place  to  place.  You  have  seen  similar  results 
in  previous  work.  Let  the  molten  globule  of  sodium  roll  off  upon  the 
floor  and  notice  what  happens. 

Compounds  of  Sodium 

6.  Caustic  Soda,  Sodium  Hydroxide,  NaOH.  —  This  com- 
pound is  prepared  by  treating  sodium  carbonate,  Na2CO3, 
in  solution  with  lime-water.     The  reaction  is 

Na2C03  +  Ca(OH)2  =  2  NaOH  +  CaCO3. 

The  calcium  carbonate,  thus  formed,  is  insoluble  in  water, 
hence  is  precipitated.  The  sodium  hydroxide  is  drawn  off, 
evaporated  to  dry  ness,  purified,  then  fused  and  molded 
into  sticks ;  in  this  form  it  is  put  upon  the  market.  It  is  a 
white  solid,  deliquescent,  with  strongly  alkaline  properties. 

7.  Sodium    Chloride,    NaCl.  —  As   already  stated,   this 
compound  occurs  very  abundantly.     In  some  places  it  is 
mined  much  as  rock  or  metallic  ores  are  mined.     In  other 


210  MODERN  CHEMIST RT 

places,  where  the  deposits  are  upon  the  surface,  mingled 
with  considerable  quantities  of  sand  and  earthy  matters,  it 
is  dissolved  out  and  the  strong  solution  evaporated.  In 
some  of  our  states  wells  are  sunk  into  the  deposits,  and 
water  pumped  in  to  dissolve  the  salt.  This  is  again  drawn 
out  and  evaporated.  In  some  places  along  the  Mediter- 
ranean the  sea  water  is  pumped  up  and  allowed  to  trickle 
down  over  brush  or  lattice  work,  whereby  it  is  much  con- 
centrated in  strength,  then  this  solution  is  evaporated  to  dry- 
ness  in  large  shallow  pans.  It  crystallizes  in  cubes,  as  may 
be  seen  if  a  strong  solution  is  allowed  to  evaporate  slowly. 

Sodium  chloride,  if  chemically  pure,  is  not  deliquescent, 
but  owing  to  impurities  present  that  which  is  generally 
put  upon  the  market  soon  becomes  damp  when  exposed  to 
the  air.  It  is  used  very  extensively  in  the  manufacture  of 
other  important  compounds  of  sodium  ;  also  largely  in  our' 
food.  A  part  of  it  is  said  to  be  decomposed  by  the  diges- 
tive fluids  of  the  stomach  and  to  form  hydrochloric  acid. 

8.  Sodium  Carbonate,  Na2C03. — This  is  a  very  impor- 
tant compound  used  in  the  manufacture  of  soap,  glass,  and 
for  a  variety  of  other  purposes.  In  the  early  part  of  the 
last  century  soda  crystals,  as  this  compound  is  often  known 
in  commerce,  sold  for  over  $300  a  ton,  while  now  the  same 
quantity  is  worth  scarcely  §20.  There  are  two  general 
processes  of  manufacture.  The  simplest  and  the  one  most 
in  favor  at  the  present  time  is  the  — 

Solvay  Process.  —  This  consists  of  passing  a  current  of  ammonia 
into  a  strong  solution  of  sodium  chloride  until  it  is  saturated ;  carbon 
dioxide  is  next  forced  in  and  with  the  ammonia  forms  ammonium 
bicarbonate.  This  reacts  with  the  common  salt,  forming  sodium 
bicarbonate.  These  processes  may  be  shown  thus  :  — 

NH4OH  +  C02  =  NH4HC03, 
NaCl  +  NH4HC03  =  NaHCO3  +  NH4C1. 


THE  ALKALI  METALS  211 

The  sodium  bicarbonate  crystallizes  out  much  more  quickly  than 
the  ammonium  chloride,  and  in  this  way  the  two  compounds  are 
separated.  The  bicarbonate  of  soda  is  then  heated  to  expel  a  portion 
of  the  carbon  dioxide,  and  sodium  carbonate  results,  thus:  — 

2  NaHCOg  +  heat  =  Na2CO3  +  CO2  +  H2O. 

This  process  is  very  cheap  because  the  salt  can  be  had  for  a  few  cents 
per  hundred  pounds,  the  ammonia  is  obtained  abundantly  from  all 
gas  factories,  and  the  carbon  dioxide  can  be  had  by  calcining  limestone 
in  making  lime.  Or,  as  seen  by  the  last  reaction  above,  the  carbon 
dioxide  driven  off  from  the  bicarbonate  of  soda  may  be  utilized  for 
this  purpose,  and  from  the  ammonium  chloride  obtained  in  the  second 
step  ammonia  may  be  evolved  by  treating  it  with  lime.  It  will  be 
seen,  therefore,  that  the  result  of  one  part  of  the  process  may  serve  in 
another  part  and  thus  reduce  the  final  cost  of  manufacture. 

The  Leblanc  Process.  —  This  is  more  complicated  than  Solvay's,  and 
more  expensive ;  hence,  were  it  not  for  the  value  of  some  by-products 
which  are  obtained,  it  would  no  longer  be  used.  It  really  consists  of 
three  steps.  First,  common  salt  is  treated  with  sulphuric  acid  and 
heated,  at  first  moderately  and  then  more  strongly.  In  the  beginning 
the  salt  is  converted  into  acid  sodium  sulphate,  thus :  — 

NaCl  +  H2SO4  =  XaHSO4  +  HC1. 

Xext,  this  acid  salt  reacts  with  another  part  of  sodium  chloride,  form- 
ing normal  sodium  sulphate,  thus :  — 

NaCl  +  NaHS04  =  Na2SO4  +  HC1; 
or,  putting  the  two  together,  we  have  — 

2  NaCl  +  H2SO4  =  NajSO4  +  2  HC1. 

The  sodium  sulphate  thus  obtained  is  called  salt  cake.  The  hydro- 
chloric acid  vapors  are  passed  into  flues,  down  which  water  constantly 
trickles  and  absorbs  the  acid.  This  is  a  valuable  by-product,  and 
serves  in  some  places  to  keep  alive  the  Leblanc  industry. 

Second,  this  salt  cake  is  mixed  with  powdered  coal  and  limestone, 
and  heated,  when  sodium  carbonate,  mixed  with  several  other  sub- 
stances, is  obtained.  The  mixture  is  black  in  color  and  is  known 
as  black  ash.  The  reaction  shows  the  chemical  changes  that  take 
place :  — 

4  -f  CaCO3  +  2  C  =  Na2CO3  +  CaS  +  2  CO2. 


212  MODERN  CHEMISTRY 

This  black  ash  is  treated  with  water  to  dissolve  out  the  sodium  car- 
bonate, and  the  solution  is  concentrated  and  purified  by  calcining, 
dissolving,  and  recrystallizing. 

In  connection  with  almost  every  Leblanc  factory  is  also  one  for  the 
manufacture  of  bleaching  powder  on  a  large  scale,  by  using  the  hydro- 
chloric acid  obtained  as  a  by-product,  with  native  manganese  dioxide. 

9.  Sodium  Nitrate,  NaN03. — This  is  known  as  Chile 
saltpeter  on  account  of  the  locality  from  which  it  is  ob- 
tained and  its  close  resemblance  to  potassium  nitrate. 
The  crude  salt  found  native 'in  Chile  is  dissolved  in 
water  and  concentrated,  whereupon  the  pure  crystals 
separate.  From  the  fact  that  it  absorbs  moisture  from 
the  air,  it  cannot  be  used  in  making  gunpowder  to  any 
great  extent.  It  is  used  largely,  however,  in  the  manu- 
facture of  nitric  acid  and  also  for  artificial  fertilizers. 

10.  Sodium  Sulphate,  Na2S04.  —  This  is  frequently  called 
Glauber's  salt.     It  is  a  white  crystalline  salt  obtained  in 
the  preparation  of  sodium  carbonate  as  described  above. 

11.  Sodium    Bicarbonate,    NaHC03. — This    is    common 
cooking   soda,    and   is   usually    prepared   by   the    Solvay 
process  of  making  soda  crystals,  hence  is  very  inexpen- 
sive.    In  making  bread  the  "  soda  "  is  put  with  some  such 
acid  as  sour  milk.     The  acetic  or  lactic  acid,  or  whatever 
it  may  be,  reacts  with  the  soda,  setting  free  carbon  dioxide, 
which  raises  the  dough  by  struggling  to  escape  through  it. 
At  the  same  time  the  acid  disappears  in  the  formation  of  a 
neutral  salt.     This  may  be  seen  by  the  following  reaction 
of  "  soda  "  with  acetic  acid  :  — 

NaHC03  +  HC2H302  =  NaC2H3O2  +  H2O  +  CO2. 

"N, 

12.  Soap.  — This  is  a  substance  which  has  been  made  in 

greater  or  less  quantities  for  probably  two  thousand  years. 
At  first,  however,  it  was  used  simply  as  an  ointment  in  a 


THE  ALKALI  METALS  213 

medicinal  way,  and  not  till  about  200  A.D.  was  it  applied 
as  it  is  to-day,  and  even  then  only  to  a  limited  extent. 
Soap  is  made  by  combining  some  alkali,  as  caustic  soda 
or  potash,  with  some  fatty  substance  or  oil.  The  fat  con- 
tains an  acid  which  combines  with  the  alkali,  hence  we  see 
that  soap  is  really  a  salt.  It  retains  some  alkaline  proper- 
ties, however,  just  as  many  other  salts  do,  simply  because 
when  dissolved  in  water  it  is  hydrolyzed,  that  is,  decom- 
posed by  the  water,  forming  caustic  soda  or  potash. 
Herein  lies  the  chemical  value  of  the  soap.  It  has  been 
said  that  soda  crystals,  Na2CO3,  are  used  in  making 
soap.  They  must  first  be  converted  into  caustic  soda, 
however,  and  this  is  done  by  treating  the  solution  with 
milk  of  lime,  Ca(OH)2,  as  described. 

13.  Hard  and  Soft  Soap.  —  We  have  two  kinds  of  soap, 
hard  and  soft;    the  former  is  made  from  sodium  com- 
pounds, the  latter  from  potassium.     Wood  ashes  contain 
considerable  quantities  of  potassium  carbonate  ;  formerly, 
these  were  saved  by  farmers,  placed  in  large  "  hoppers," 
lime  added,  and  then  leached.     A  dark-colored,  strongly 
alkaline  solution  filtered  out,  containing  a  considerable  per- 
centage of  caustic  potash.     This  was  treated  with  waste 
fat,  and  boiled,   when  in  the  course  of  a  few  hours  a 
strongly  alkaline  soft  soap  was  obtained,  which  always 
remained  pasty.     By  adding  common  salt  to  this,  it  could 
be  converted  into  a  dark-colored  solid  mass  ;    for  many 
years  this  was  the  only  hard  soap  known.     Sodium  com- 
pounds  yield   hard   soap   directly   on    combination  with 
fats,  hence  they  are  most  used  at  the  present  time  in  the 
manufacture  of  ordinary  hard  soap. 

14.  The  practical  value  of  soap  lies  in  the  fact  that  on 
account  of  its  slightly  alkaline  properties  it  has  the  power 
of  uniting  with  the  oil  secreted  by  the  glands  of  the  skin, 


214  MODERN  CHEMISTRY 

and  which  holds  the  particles  of  foreign  matter  ;  this 
"dirt,"  therefore,  may  be  removed  by  the  mechanical 
action  of  the  water.  This  also  explains  why  frequent 
bathing  with  the  application  of  strong  soap  will  tend  to 
cause  the  skin  to  chap,  by  the  removal  of  the  oil  which 
keeps  it  soft  and  pliable. 

15.  Test  for  Sodium.  —  Sodium  may  always  be  detected 
by  what  is  known  as  the  flame  test. 

EXPERIMENT  130.  —  Heat  a  platinum  wire  in  the  Bunsen  flame 
until  it  no  longer  imparts  any  color  to  the  flame.  Then  dip  it  into 
the  sodium  solution  and  again  hold  in  the  flame.  The  bright  yellow 
color  is  distinctive. 

POTASSIUM  :  K  =  39 

16.  Where  found.  —  Because  of   its   great  affinity  for 
other  substances,  potassium  never  occurs  free.     It  is  very 
widely  distributed,  however,  in  the  form  of  compounds ; 
it  is  a  constituent  of  many  rocks,  and  by  their  decomposi- 
tion becomes  a  part  of  various  soils.     Being  stored  up  by 
plants  it  enters  into  the  animal  economy,  and  by  some  ani- 
mals, especially  sheep,  it  is  exuded  from  the  skin  and  col- 
lects in  considerable  quantities  upon  the  wool  in  an  oily 
substance  called  suint. 

17.  How  obtained  in  Metallic  Form.  —  Potassium,  like 
sodium,  may  be  obtained  by  electrolysis,  but  is  usually 
reduced  by  treating  caustic  potash  with  charcoal.     The 
reaction  shows  the  chemical  changes  :  — 

6  KOH  +  2  C  =  2  K2CO3  +  3  H2  +  Ka. 

The  potassium  distills  out  and  is  collected  under  oil. 

18.  Characteristics  of  Potassium.  —  It  is  a  metal  some- 
what softer  than  sodium ;  has  a  bright  luster  and  white 
color,  but  it  tarnishes  instantly  when  cut  in  the  air,  so 
great  is  its  affinity  for  oxygen  and  moisture.     At  zero  it 


THE  ALKALI  METALS  215 

becomes  crystalline  in  structure,  hard,  and  brittle.  When 
thrown  upon  water  it  immediately  begins  to  decompose 
the  water,  and  with  such  energy  that  it  is  melted  and 
the  hydrogen  given  off  is  ignited,  burning  with  a  violet 
color.  This  is  due  to  the  vaporization  of  a  small  portion 
of  the  potassium.  As  hydrogen  is  set  free  from  the  water 
caustic  potash  is  formed,  according  to  a  reaction  previously 
seen  :  -  H,O  +  K  =  KOH  +  H. 

With  the  halogens,  chlorine  and  bromine,  potassium 
ignites  spontaneously,  and  with  liquid  ammonia  it  forms  a 
blue  solution.  It  possesses  all  the  strong  alkaline  charac- 
teristics of  sodium  in  a  degree  even  more  marked. 

19.  In  the  metallic  form  potassium  has  no  uses  in  the 
arts.     Its  compounds,  however,  are  very  valuable.     Any 
potassium  salt  may  be  tested  in  the  same  way  as  are  the 
sodium   compounds,   with  a  platinum  wire.     The  violet 
flame  is  characteristic.     If  both  sodium  and  potassium  are 
present  it  will  be  necessary  to  observe  the  flame  through 
a  blue  glass.       This  transmits  the  potassium  rays,  but 
absorbs  those  of  the  sodium. 

Compounds  of  Potassium 

20.  Potassium  Hydroxide  or  Hydrate,  KOH.  —  In  earlier 
days  the  most  common  source  of  potassium  compounds 
was  wood  ashes,  which  were  boiled  with  water   in   iron 
pots.     The  potassium  salts  were  dissolved  out  in  this  man- 
ner, and  from  them  was  prepared  caustic  potash,  KOH. 
This  is  now  obtained  by  a  method  similar  to  that  used  in 
the  preparation  of  caustic  soda,  viz.  by  treating  potassium 
carbonate  with  milk  of  lime,  Ca(OH)2,  when  this  reaction 
takes  place  :  — 

K2CO3  +  Ca(OH)2  =  2  KOH  +  CaCO3. 


216  MODERN  CHEMISTRY 

The  latter  compound  is  insoluble  and  is  precipitated  ;  the 
former  is  drawn  off,  concentrated,  purified  by  redissolving 
in  alcohol,  again  dried,  fused  and  molded  in  the  familiar 
round  sticks.  It  is  very  deliquescent,  and  quickly  dis- 
solves in  the  moisture  it  obtains  from  the  air.  It  is  used 
largely  as  a  reagent  in  the  laboratory. 

21.  Potassium  Carbonate,  K2C03. — As  already  indicated, 
this  was  at  one  time  obtained  almost  exclusivjely  from  the 
ashes  of  wood.     These  were  treated  with  water,  by  which 
the  potassium  carbonate  was  dissolved  out ;  the  solution 
was  boiled  dry,  forming  a  white  salt  known  as  pearl  ash. 
Now  large  quantities  are  obtained  by  washing  sheep's  wool 
in  hot  water,  then  drawing  off  the  greasy  products  obtained 
and  heating  them  very  strongly  to  expel  the  oil.     The 
potash  salts  remain  and  are  dissolved  out  by  water. 

Another  source  of  considerable  quantities  is  the  beet- 
sugar  industry.  The  beet  sap  is  boiled  down  to  a  sirup, 
and  from  this  sirup  is  extracted  the  sugar,  leaving  a  sort 
of  molasses,  in  which  still  remain  the  potassium  compounds 
that  the  beets  had  obtained  from  the  soil.  This  is  gen- 
erally first  fermented  and  distilled;  the  residue  is  boiled  to 
dry  ness  and  calcined.  Then  from  the  ashes  the  potash 
salts  are  obtained  by  lixiviation. 

Potassium  carbonate  may  be  prepared  from  the  chloride 
by  the  Leblanc  process. 

22.  Potassium  Chlorate,  KC103.  —  This  is  a  white,  crys- 
talline salt,  often  sold  under  the  misleading  name  potash. 
It  has  a  not  unpleasant,  cooling  taste,  and  is  used  some- 
what for  throat  affections.     In  the  laboratory  it  has  num- 
berless applications,  many  of  which  are  familiar  to   the 
student.     In  the  arts  it  is  used  in  making  matches,  for 
fireworks,  etc.     It  is  prepared   by   passing  a  current   of 
chlorine  into  a  solution  of  caustic  potash,  by  which  both 


THE  ALKALI  METALS  217 

potassium  chloride  and  potassium  chlorate  are  formed. 
The  former  is  much  more  soluble,  hence  in  concentrating 
the  solution  the  potassium  chlorate  will  crystallize  out 
first,  leaving  the  chloride  still  in  solution. 

23.  Potassium  Nitrate,  KN03. — This  is  commonly  known 
as  saltpeter.     It  is  a  white,  crystalline  salt,  found  native 
in  various  parts  of  the  world.     As  we  have  seen,  it  is  pro- 
duced by  the  decomposition  of  organic  matter,  especially 
the  refuse  from  stables.     This  decomposition  is  supposed 
to  be  brought  about  by  the  presence  of  certain  bacteria, 
and  in  some  countries  the  process  is  now  carried  on  artifi- 
cially to  a  considerable  extent. 

24.  The  refuse  is  mixed  with  ashes  and  lime,  and  fre- 
quently stirred  to  increase  the  rapidity  of  decomposition. 
After  a  time  the  whole  is  leached  with  water  to  dissolve 
out  the  nitrate.    The  solution  thus  obtained  is  concentrated 
and  the  salt  allowed  to  crystallize. 

Considerable  quantities  are  now  made  by  treating  sodium 
nitrate,  which  occurs  in  almost  inexhaustible  quantities  in 
Chile,  with  potassium  chloride,  whereby  this  double  reac- 
tion takes  place  :  — 

KC1  +  NaN03  =  KN03  +  NaCl. 

Potassium  nitrate  is  used  extensively  in  making  gun- 
powder. 

25.  Potassium  Iodide,  KI.  — This  is  a  white  crystalline 
salt.     It  is  used  frequently  in  the  laboratory  as  a  reagent, 
and  to  some  extent  in  medicine. 

26.  Potassium  Bromide,  KBr.  —  This  is  a  white  salt, 
very  similar  in-  general  appearance  to  the  iodide.     It  is 
used  frequently  in  medicine  as  a  sedative. 

EXPERIMENT  131.  —  Take  any  potassium  solution  and  make,  the 
flame  test  just  as  you  did  for  sodium  in  Experiment  130.  Notice 


218  MODERN  CHEMISTRY 

color  of  the  flame.  Now  mix  with  it  a  solution  of  some  sodium  com- 
pound, and  again  test.  Can  you  see  the  potassium  flame?  Next 
observe  the  flame  through  a  sheet  of  blue  glass.  State  results. 

COMPARATIVE  REVIEW  OF  THE  ALKALI  METALS 

Sodium  and  Potassium. 

As  found  in  nature  —  Two  important  native  compounds  of  each  — 

Where  found. 

Which  the  more  important. 
Comparison  of  the  two  metals. 
Color. 

Tendency  to  oxidize. 
Hardness. 
Affinity  for  water. 
Melting  point. 
Affinity  for  the  halogens. 
Experiments  that  illustrate  most  of  these  properties. 

Proof  that  hydrogen  is  set  free  from  water  by  these  metals. 
Proof  of  the  hydroxide  formed. 
Compounds. 

The  Hydroxides  —  Method  of  preparing  —  Reactions. 

Usual  form  —  Appearance  —  Properties —  Uses. 
The  Carbonates  —  Source  of  supply. 

Former  method  of  obtaining  K2CO8. 
Present  sources. 

Two  methods  of  preparing  Na2CO3. 
Uses  of  the  carbonates. 
Review  work  in  glass. 
Kinds  of  glass  —  Differences. 
Soap  making  —  Chemistry  of. 

Kinds  of  soap. 
Common  salt. 

Preparation  for  market. 
Cooking  soda  —  Chemical  name  and  formula. 

Chemistry  of  in  bread  making. 
Saltpeter  —  Chemical  name  and  formula,. 

Preparation  —  Appearance  —  Uses. 
Potassium  chlorate  —  Formula. 
Appearance  —  Uses, 


CHAPTER   XIX 

THE  ALKALINE  EARTHS 
MAGNESIUM  :  Mg  =  24 

1.  Occurrence.  —  Magnesium  in  the  form  of  certain  com- 
pounds is  widely  distributed.     Among  the  most  important 
of  its  compounds  may  be  named  the  familiar  minerals, 
asbestos  and  meerschaum.     The  first  is  a  silicate  of  magne- 
sium and  aluminum,  and  the  second  a  silicate  of  magnesium. 
Magnesium  limestone,  or  dolomite,  CaMg(CO3)2,  occurs  in 
considerable  quantities. 

2.  Peculiarities  of  the  Metal.  —  Magnesium   is  silvery 
white  in  color,  and  melts  at  a  red  heat.     In  dry  air  it  does 
not  tarnish,  but  moisture  quickly  affects  it.      While  at 
ordinary  temperatures  it  is  slightly  brittle,  as  it  nears  the 
melting  point  it  becomes  malleable  and  may  be  drawn  into 
wires.     These,  flattened  into  ribbons,  are  the  usual  com- 
mercial form,  though  the  powder  is  also  frequently  seen. 
The  metal  is  easily  ignited  and  burns  with  a  dazzling 
white  light,  rich  in  actinic  properties.     This  combustion 
is  so  vigorous  that  it  will  decompose  even  carbon  dioxide 
and  certain   other  similar  oxides.     (See  carbon  dioxide, 
page  143.) 

3.  Uses.  —  On  account  of  the  light  furnished  by  burn- 
ing magnesium,  it  is  frequently  used  in  taking  flash-light 
pictures  of  caverns,  and  other  interior  views.     It  is  like- 
wise used  to  a  limited  extent  in  making  fireworks.     In 
the  form  of  a  powder  it  is  often  used  like  zinc  in  the 

219 


220  MODERN  CHEMISTRY 

reduction  of  ferric  to  ferrous  salts  (see  page  307),  on 
account  of  the  rapidity  with  which,  in  the  presence  of  sul- 
phuric or  hydrochloric  acid,  it  yields  hydrogen.  It  is 
also  used  by  chemists  in  cases  of  supposed  arsenic  poison- 
ing, in  making  Marsh's  test.  Zinc  nearly  always  contains 
traces  of  arsenic,  whereas  magnesium  is  obtained  prac- 
tically pure  ;  for  this  reason  it  is  substituted  for  the  zinc. 

Compounds  of  Magnesium 

4.  Magnesium   Sulphate,    MgS04.  —  One   of    the   most 
common  compounds   is   epsom  salts,  magnesium  sulphate, 
MgSO4,  7  H2O.     This  is  a  salt  found  in  the  water  of  many 
mineral  springs.     It  has  a  very  bitter  taste  and  is  used 
largely  in  medicine,  also  extensively  in  finishing  cotton 
goods. 

5.  Magnesia,  Magnesium  Oxide,  MgO.  —  This  is  a  white 
solid  obtained  when  magnesium  is  burned  in  the  air  or  in 
oxygen.     It  is  often  prepared  by  heating  magnesium  car- 
bonate to  expel  the  carbon  dioxide,  just  as  lime  is  pre- 
pared from  limestone  (see  lime,  page  221).      The  reaction 
is  seen  below  :  — 

MgCO3  +  heat  =  MgO  +  CO2. 

It  is  used  as  a  face  powder,  and,  because  of  its  high  melt- 
ing point,  sometimes  for  making  or  lining  crucibles. 

CALCIUM:  Ca  =  40 

6.  Occurrence.  —  In  the  form  of  compounds,  calcium  is 
one  of  the  most  abundant  and  most  widely  distributed 
elements  known.     Because  of  its  strong  affinity  for  water, 
however,  it  never  occurs  free.     The  carbonate  of  calcium, 
CaCOg,  is  the  most  abundant  form  and  includes  many  well- 


THE  ALKALINE  EARTHS  221 

known  substances,  such  as  marble,  limestone,  and  chalk. 
Some  of  the  more  highly  crystallized  forms  are  Iceland 
spar,  calcite,  and  dog-tooth  spar,  while  stalactites,  corals, 
and  shells  have  the  same  composition.  The  next  most 
abundant  natural  compound  of  calcium  is  gypsum,  calcium 
sulphate,  CaSO4,  2  H2O. 

7.  Production  of  the  Metal.  —  Calcium  has  seldom  been 
prepared,  and  then  only  for  the  purpose  of  studying  its 
properties.     Sir  Humphry  Davy,  who  first  isolated  potas- 
sium and  sodium  from  their  hydroxides  by  means  of  an 
electric  current,  in   the  same  way   decomposed   calcium 
chloride  and  obtained  calcium  in  the  metallic  form. 

8.  Characteristics.  — Calcium  is  of  a  brassy  yellow  color, 
and  somewhat  malleable  and  ductile.     It  has  a  density  of 
about   1.6,  and   like  sodium   readily   decomposes  water, 
forming  the  hydroxide,  Ca(OH)2.     It  is  readily  soluble  in 
dilute  acids,  and  at  a  temperature  a  little  above  its  melt- 
ing point  it  burns  with  a  reddish  yellow  light.     The  cost 
of  its  production  is  too  great  to  admit  of  any  practical 
use. 

Compounds  of  Calcium 

9.  Although  as  a  metal  calcium  is  of  so  little  value,  it 
would  be  difficult  to  estimate  the  worth  of  the  compounds. 

10.  Lime,  Calcium  Oxide,  CaO.  —  This  is  one  of  the 
most  important  compounds  known.  It  is  easily  prepared 
from  limestone  by  heating  it  to  a  red  heat,  at  which  tem- 
perature carbon  dioxide  is  expelled,  thus:  - 

CaCO3  +  heat  =  CaO  +  CO2. 

Lime  is  prepared  in  kilns,  which  are  simply  square  rooms 
or  ovens  15  to  20  feet  high,  and  10  to  15  feet  each  way. 
See  Fig.  52.  The  limestone  is  thrown  in  from  above  and 


222 


MODERN  CHEMISTRY 


strongly   heated   with   dry  cordwood   or   coke   in   alter- 
nate layers.      In  a  few  days  the  limestone  is  converted 

into  lime,  then  the  fire  is 
removed,  the  mass  is  allowed 
to  cool  and  the  lime  with- 
drawn, and  if  intended  for 
shipment  packed  in  barrels. 
Some  kilns  are  arranged 
below  so  as  to  enable  the 
workmen  to  remove  the 
lime  without  putting  out 
the  fire.  Such  are  contin- 
«te  uously  ^d  from  above,  and 

'    the  operation  goes  on  with- 
FlG-  52'  out  ceasing. 

11.  Properties  of  Lime.  —  Prepared  as  above  it  is  in  the 
form  of  white  lumps,  but  if  left  exposed  to  the  air  it 
begins  at  once  to  take  up  moisture  and  in  a  short  time 
crumbles  to  a  fine  powder.     It  is  then  said  to  be  "air- 
slaked,"  although  it  is  really  the  water  in  the  air  that  has 
caused  the  change.     The  reaction  is  as  follows  :  — 

CaO  +  H2O  =  Ca(OH)2. 

12.  If  a  lump  of  freshly  prepared  lime  be  treated  with 
water,  the  change  indicated  above  takes  place  rapidly, 
accompanied  by  the  evolution  of  considerable  heat.     The 
hydroxide,  Ca(OH)2,  thus  obtained  is  soluble  in  water, 
though  very  much  less  so  than  ordinary  caustic  soda  or 
potash.     The  solution  of  caustic  lime  is  known  as  lime- 
water. 

13.  Uses  of  Lime.  —  Lime  is  indispensable  in  the  erec- 
tion of  almost  all  structures.     Mixed  with  sand  it  forms 
the  mortar  for  nearly  all  stone  and  brick  work  —  except 


THE  ALKALINE  EARTHS  223 

such  as  is  laid  under  water  —  and  much  of  the  plaster  for 
indoor  work.  Unmixed  with  sand  it  is  frequently  used 
to  give  the  white  or  finishing  coat  in  plastering,  though 
various  plasters  are  now  beginning  to  take  the  place  of 
ordinary  lime  in  this  respect. 

14.  It  is  also  used  extensively  in  the  lime  purifiers  of 
illuminating  gas  works,  in  the  manufacture  of  bleaching 
powder,  of  ammonia,  in  removing  the  hair  from  hides  in 
the  process  of  tanning,  and  for  numerous  other  purposes 
where  a  cheap  and  easily  prepared  alkali  is  demanded. 

15.  Calcium  hydroxide,  exposed  to  the  air,  absorbs  car- 
bon dioxide  and  forms  calcium  carbonate,  thus :  — 

Ca(OH)2  +  C02  =  CaC03  +  H2O. 

The  same  reaction  takes  place  in  mortar,  hence  that  which 
has  been  properly  prepared  will  grow  gradually  harder, 
in  time  being  converted  back  again  into  a  siliceous  lime- 
stone. If  a  beaker  containing  lime-water  be  left  exposed 
to  the  air,  in  a  little  while  a  white  film  will  be  seen  to 
cover  the  surface  of  the  liquid.  This  is  really  a  pre- 
cipitate of  calcium  carbonate,  resulting  from  the  absorp- 
tion of  the  carbon  dioxide  of  the  air  by  the  lime-water. 
If  the  breath  from  the  lungs  be  blown  through  a  clear 
solution  of  lime-water,  it  quickly  becomes  clouded  from 
the  same  cause. 

16.  Calcium  Carbonate,  CaC03.  —  In  the   natural   form 
this  is  known  in  the  several  varieties  mentioned  above. 
Artificially,  it  may  be  prepared  as  a  white  precipitate  by 
adding  some  alkaline  carbonate,  as  sodium  or  ammonium 
carbonate,  to  a  calcium  chloride  solution.     The  following 
reaction  takes  place  :  — 

CaCl2  +  (NH4)2CO3  =  2  NH4C1  +  CaCO3. 


224  MODERN   CHEMISTRY 

It  is  insoluble  in  pure  water,  but  when  an  excess  of  carbon 
dioxide  is  present,  it  slowly  dissolves. 

EXPERIMENT  132.  —  Through  a  few  cubic  centimeters  of  lime-water 
in  a  flask  or  beaker,  pass  a  current  of  carbon  dioxide,  or  blow  the 
breath  for  some  time.  What  finally  becomes  of  the  white  precipitate 
which  forms  at  first?  Preserve  the  water. 

In  this  way  water  charged  with  carbon  dioxide  percolating  through 
limestone  rocks  gradually  dissolves  them,  and  has  formed  many  of  the 
great  caves  known  in  this  country.  This  same  water,  dripping  from 
the  roof  of  caverns,  being  no  longer  under  pressure,  gives  up  its  carbon 
dioxide,  and  the  calcium  carbonate,  no  longer  held  in  solution  by  the 
gas,  is  deposited  in  the  form  of  stalactites  and  stalagmites. 

17.  Calcium  Chloride,  CaCl2.  — This  is  a  white  salt  which 
may  be  prepared  from  any  form  of  the  carbonate  by  treat- 
ing with  hydrochloric  acid.     It  is  a  by-product  formed  in 
the  preparation  of  carbon  dioxide  from  limestone  :  — 

CaC03  +  2  HC1  =  CaCl2  +  CO2  +  H2O. 

It  is  strongly  deliquescent,  and  is  often  used  in  drying 
gases,  damp  cellars,  etc. 

18.  Calcium  Sulphate,  CaS04,  2  H20.  —  In  the  natural 
form  this  is  the  gypsum  already  mentioned.      It  occurs 
in  vast  quantities  in  many  of  our  states,  notably  Kansas, 
New  York,  Illinois,  etc.,  both  in  the  form  of  rich,  heavy 
deposits,  and   mixed  with  various   impurities   upon   the 
surface.      It   is   used   extensively  in    making  plaster   of 
Paris.     This  is  manufactured  simply  by  strongly  calcining 
the  powdered  gypsum  till  half  the  water  of  crystallization 
is  expelled.     During  this  time,  as  the  water  escapes  from 
the  powdered  mass,  the  whole  seems  to  boil  vigorously. 
After  two  or  three  hours  the  process  is  complete,  and  the 
plaster  is  ready  to  be  mixed  with  the  "  retarder,"  if  neces- 
sary.   This  plaster  has  the  property  of  "  setting  "  or  hard- 


THE  ALKALINE  EARTHS  225 

ening  quickly  when  water  is  added  to  it.  This  is  due  to 
tlie  fact  that  the  anhydrous  salt  again  takes  up  the  water 
of  crystallization  expelled  in  the  previous  calcination.  If 
the  -plaster  which  has  been  used  once  be  again  calcined, 
it  acquires  again  its  property  of  "setting." 

19.  Uses  of  Plaster  of  Paris.  —  It  is  employed  extensively 
in  making  molds  for  many  of  the  finer  castings,  in  dental 
work  and  surgery,  for  statuettes,  as  a  finishing  coat  in 
plastering,  and  for  stucco  and  other  ornamental  work  on 
the  interior  of  buildings.     For  most  purposes,  a  plaster 
that  does  not  harden  so  rapidly  is  desirable,  hence  it  is 
customary  to  mix  with  it  some  kind  of   clay,  or  other 
substance,  which  causes  it  to  "set"  more  slowly.     This 
clay  has  already  been  spoken  of  as  the  "retarder." 

20.  Cements.  —  Cements  are  a  species  of  lime  which 
have   the   power   of   hardening   or   setting   rapidly,  like 
plaster  of  Paris.     They  are  prepared  by  calcining  lime- 
stone,  which  contains  a  large  percentage  of   silica  and 
alumina,  SiO2  and  A12O3.     Dolomitic  or  magnesium  lime- 
stones, containing  also  the  silica  and  alumina,  when  cal- 
cined, produce  a  cement  that  will  harden  under  water, 
known  as  hydraulic  cement.       It   has  been  stated   that 
ordinary  plaster  hardens  by  the  absorption  of  carbon  diox- 
ide from  the  air,  forming  again  calcium  carbonate.     This 
is,  necessarily,  a  slow  process.     Cements,  as  already  stated, 
are  produced  by  driving  out  the  water  of  crystallization ; 
hence,  when  they  are  mixed  with  water  for  use,  they  very 
rapidly  take  this  up  again,  forming  practically  the  original 
rock.     Hydraulic  cement  is  used  in  laying  the  piers  of 
bridges,  building  jetties,  and  other  work  that  is  to  be 
under  water.     Ordinary  cements  are  used  extensively  for 
laying   pavements,   building   roadbeds,    for   the   concrete 
foundation  for  various  kinds  of  masonry,  etc.     The  fol- 


226 


MODERN  CHEMISTRY 


lowing  shows  the  composition  of  some  cement  rocks  from 
various  localities :  — 


LOCALITY 

CaC03 

MgC03 

Si02 

Fe203 

A1,0, 

H20 

UNDETER- 
MINED 

Rosendale,  N.Y. 

45.91 

26.14 

15.37 

11.38 

1.20 

Utica,  111. 

42.25 

31.98 

21.12 

1.12 

1.07 

2.46 

Milwaukee,  Wis. 

45.54 

32.46 

17.56 

3.03 

1.41 

Cement,  Ga. 

43.50 

22.00 

22.10 

1.80 

5.45 

4.95 

Siegfried,  Pa. 

78.90 

2.66 

11.62 

6.25 

0.55 

Ft.  Scott,  Kan. 

73.95 

2.26 

18.75 

2.32 

2.15 

0.37 

0.20 

Ft.  Scott,  Kan.,  No.  2 

65.21 

10.65 

15.21 

4.56 

4.37 

21.  Hard  Water.  —  Hardness  in  water  is  due  to  the 
presence  of  certain  salts  in  solution,  very  commonly  some 
compounds  of  calcium.  This  hardness  may  be  either  tem- 
porary or  permanent,  according  as  it  may  be  removed  by 
boiling  or  by  adding  ammonia,  or  not  at  all. 

EXPERIMENT  133.  —  Prepare  a  soap  solution  by  dissolving  a  shaving 
of  soap  in  warm  distilled  water.  Allow  it  to  stand  a  few  minutes.  It 
should  be  perfectly  clear.  To  a  few  cubic  centimeters  of  the  lime- 
water,  through  which  the  breath  was  blown  till  clear  again,  add  a 
little  of  the  soap  solution.  What  happens?  Why?  Take  another 
portion  of  the  clear  lirne-water  and  boil  it  for  a  few  minutes.  Has 
any  sediment  formed  in  the  flask  ?  The  heat  has  expelled  the  carbon 
dioxide ;  why  does  the  precipitate  form  ?  Decant  a  portion  of  it  and 
test  with  the  soap  solution :  is  the  water  still  "  hard  "  ?  What  effect 
has  the  boiling  had  ? 

To  another  portion  of  the  same  hard  water  (which  has  not  been 
boiled)  add  a  few  drops  of  ammonia  and  again  test  to  see  whether  the 
water  is  still  hard.  What  are  the  results? 

Add  a  little  powdered  calcium  sulphate,  CaSO4,  to  some  water,  and 
after  some  time  test  a  portion  of  it  to  learn  whether  it  is  hard. 
Now  try  to  remove  the  hardness  by  the  methods  previously  used. 
State  results. 


THE  ALKALINE  EAETHS  227 

22.  Water  the  hardness  of  which  may  be  easily  re- 
moved is  said  to  be  temporarily  hard,  while  that  which 
cannot  be  so  changed  is  permanently  hard.      When  the 
hands  are  washed  with  soap  in  hard  water,  the  soap  pre- 
cipitates the  salts  in  the  water,  of  which  a  portion  settles 
upon  the  skin,  giving  it  an  unpleasant  feeling.     Another 
part  of  the  precipitate  is  usually  seen  as  a  scum  upon  the 
surface  of  the  water. 

23.  Bleaching  Powder,  Ca(C10)2  +  CaCl2.  —  This  is  also 
called  hypochlorite  of  lime.     It  is  a  white  powder  which 
is  prepared  by  passing  chlorine  into  chambers  containing 
common  lime  spread  loosely  upon  shelves.     The  reaction 
may  be  represented  thus  :  — 

2  CaO  +  2  C12  =  Ca(ClO)2  +  CaCl2. 

When  treated  with  any  dilute  acid,  chlorine  is  again  set 
free  ;  for  this  reason  the  compound  is  used  extensively  as 
a  source  of  chlorine  in  bleaching  muslin  and  other  cotton 
goods.* 

24.  From  the  fact  that  chlorine  does  not  bleach  dry 
cloth,  it  is  believed  to  be  not  the  direct  bleaching  agent, 
but  simply  that  which  sets  free  another.     It  will  be  seen 
later,  in  studying  the  compounds  of  manganese,  that  log- 
wood, litmus,  and  other  colored  vegetable  solutions  are 
rapidly  bleached  by  the  use  of  potassium  permanganate, 
in  the  presence  of  some  acid.      Experiment  shows  that 
this  is  due  to  the  oxygen  that  is  set  free  from  the  per- 
manganate.    Similarly  the  chlorine,  which  has  most  won- 
derful affinity  for  hydrogen  (see  page  108),  sets  free  the 
oxygen  from  the  water  with  which  the  cloth  is  moistened, 
and  this  in  the  nascent  state  oxidizes  the  coloring  matter 
and  converts  it  into  colorless  compounds. 

*  See  wo  A  under  Chlorine,  page  111. 


228  MODERN  CHEMISTRY 

25.  When  a  current  of  carbon  dioxide  is  passed  through 
a  solution  of  bleaching  powder,  chlorine  is  liberated,  and 
can  be  detected  by  the  odor,  just  as  when  treated  as  above 
with  a  dilute  acid.     Exposed  to  the  air,  bleaching  powder 
yields  up  its  chlorine,  owing  to  the  action  of  the  carbon 
dioxide  always  present ;  but  naturally  the  process  is  very 
slow.     On  account  of  this  fact,  and  because  chlorine  is  an 
excellent  germicide  and  disinfectant,  bleaching  powder  is 
used  frequently  in  sick  rooms  and  hospital  wards.     The 
generation  of  the  chlorine  is  so  slow  as  to  be   scarcely 
noticeable,  and  yet  sufficient  to  keep  the  atmosphere  in 
a  wholesome  condition. 

STRONTIUM  :  Sr  =  87 

26.  Its  Name.  —  Strontium  is  a  rare  metal,  which  re- 
ceived its  name  from  Strontian,  a  place  in  Scotland,  where 
it  was  discovered.     One  of  its  chief  sources  is  the  mineral 
strontianite,  SrCO3. 

Compounds  of  Strontium 

27.  Strontium  Nitrate,  Sr(N03)2.  — This  is  a  white  crys- 
talline salt,  soluble  in  water.     It  is  used  considerably  in 
fireworks  and  in  making  "  red  fire." 

EXPERIMENT  134.  —  Mix  thoroughly  about  a  gram  each  of  stron- 
tium nitrate  and  potassium  chlorate,  finely  pulverized,  and  about  as 
much  in  bulk  of  powdered  shellac.  Place  the  mixture  in  an  iron 
saucer  and  ignite  with  a  match.  State  the  results. 

28.  Strontium  Carbonate,  SrC03.  —  This  is  a  white  pre- 
cipitate, like  calcium  carbonate,  obtained  when  ammonium 
or  sodium  carbonate  is  added  to  a  neutral  or  alkaline 
solution  of  a  strontium  salt. 

Sr(N03)2  +  (NH4)2C03  =  SrCO3  +  2  NH4NO3. 


THE  ALKALINE  EARTHS  229 

29.  Strontium  Hydroxide,  Sr(OH)2.  —  When   water   is 
added  to  strontium  oxide,  SrO,  like   lime,  it   is   slaked, 
evolves  much  heat,  and  is  converted  into  the  hydroxide, 
Sr(OH)2.       In  this  form  it  is  used  considerably  in  the 
manufacture  and  refining  of  beet  sugar. 

BARIUM  :   Ba  =  137 

30.  Its  Name.  —  This  metal,  also  rare,  received  its  name 
from  a  Greek  word,  meaning  heavy,  and  was  so  called  be- 
cause its  chief  natural  ore,  barite,  BaSO4,  has  great  den- 
sity.    It  is  also  found  as  a  carbonate,  BaCO3,  known  as 

witherite. 

Compounds  of  Barium 

31.  Barium  Chloride,  BaCl2.  —  This  is  a  white  crystal- 
line salt,   readily  soluble  in  water.      It  is  used   in   the 
laboratory  in  testing  for  sulphuric  acid. 

32.  Barium  Sulphate,  BaS04. — This  is  a  heavy  white 
precipitate,  insoluble  in  water  and  acids.     It  is  easily  pre- 
pared by  adding  sulphuric  acid  or  any  soluble  sulphate  to 
a  solution  of  barium  chloride.     It  is  used  considerably  as 
an  adulterant  for  white  lead  (see  page  280),  and  to  some 
extent  in  weighting  paper. 

33.  Barium  Carbonate,  BaC03.  —  This  is  a  white  precipi- 
tate formed  when  ammonium  or  sodium  carbonate  is  added 
to  a  neutral  or  alkaline  solution  of  a  barium  salt.     It  is 
insoluble  in  water,  but  soluble  in  weak  acids. 

EXPERIMENT  135.  —  Let  the  student  prepare  both  of  the  above 
compounds,  using  barium  chloride  for  the  barium  solution.  Note  the 
differences  between  the  two  and  test  their  solubility  in  the  common 
acids.  State  results. 

34.  Barium  Nitrate,  Ba(N03)2. — This  is  a  white  crystal- 
line salt.      It   is   used    to  a  considerable  extent  in  the 
making  of  green  fire  for  fireworks. 


230  MODERN  CHEMISTRY 

EXPERIMENT  136.  —  Repeat  Experiment  134,  substituting  barium 
nitrate  for  the  strontium  nitrate,  and  state  results.  Sulphur  or  pow- 
dered charcoal  may  be  used  instead  of  the  shellac,  but  the  sulphur 
yields  very  irritating  fumes  of  the  dioxide,  and  the  charcoal  does  not 
burn  so  readily. 

35.  Barium  Hydroxide,  Ba(OH)2.  — This  is  a  compound 
obtained   from   barium   oxide,   BaO,  by  the  addition  of 
water,  just   as   slaked   lime  is  prepared.      Like  calcium 
hydroxide,  it  forms  a  precipitate  of  the  carbonate  upon 
the  addition  of  carbon  dioxide.     It  was  formerly  used 
extensively  in   clarifying   beet  sugar,  but  as  it  is  very 
poisonous,  and  traces  of  it  sometimes  remain  in  the  sugar, 
its  use  has  been  supplanted  by  that  of  strontium  hydroxide. 

36.  Flame  Tests.  —  The  metals  of  this  group,  calcium, 
strontium,  and  barium,  may  be  detected  by  the  flame  test. 

EXPERIMENT  137.  —  Just  as  you  tried  sodium  and  potassium,  now 
take  some  solutions  of  these  three  metals  and  make  the  flame  test  in 
the  same  way.  State  results  as  to  color  and  duration  of  flame. 

REVIEW   OF  WORK  IN  ALKALINE   EARTH  METALS 

Magnesium,  Calcium,  Strontium,  Barium. 

1.  Occurrence  —  Compare  native  compounds. 

Crystallized  forms  of  calcium  compounds. 
Uncrystallized  forms. 
Special  forms. 

2.  Artificial  compounds. 

a.  The  Oxides  of  Mg,  Ca,  Sr,  Ba. 

Wherein   is    their    preparation    similar?     Why  are 

such  compounds  used  ? 
Importance  of  CaO  and  MgO. 

b.  The  Hydroxides  —  Similarity  of  preparation. 

Uses  of  Ca(OH)2  and  Sr(OH)2. 

Preparation  of  mortar;    chemical  change  it  under- 
goes as  it  hardens. 
Hydraulic  cement ;  other  cements  ;  uses ;  explanation. 


THE  ALKALINE  EARTHS  231 

c.  The  Nitrates  —  Use  in  the  arts  of  Sr(N03)2;  Ba(N03)2. 

How  used. 
Chemical  action  of  each  constituent. 

d.  The  Sulphates —  Two  important  ones. 

Preparation  of  Plaster  of  Paris  —  Compare  with  prepa- 
ration of  CaO. 

Uses  of  CaSO4  and  BaSO4. 

Chemical  change  which  takes  place  when  Plaster  of 
Paris  hardens. 

Compare  with  hardening  of  mortar. 

e.  Hard  Waters  —  Due  to  what  compounds. 

Two  classes,  how  different. 
Methods  of  softening  water. 
Chemistry  of  these  methods. 
/    Some  special  calcium  compounds. 

CaF2 — Use,  and  method  of  using. 
Bleaching  powder  —  Uses  —  Compare  Cl  and   SO2  as 
bleaching  agents  —  Chemical  action  of  each. 

Use  of  bleaching  powder  as  a  disinfectant  — 
How  is  chlorine  set  free  ? 

3.  Flame  tests  —  Method  of  making  test. 

Comparison  of  colors  imparted. 

4.  Comparative  value  of  the  metals  in  metallic  form. 

5.  Exercise  —  Given  some  marble,  HC1,  H2SO4,  H2O,  and  Na2COs. 

Tell  how  to  prepare  CaO,  Ca(OH)2,  CaSO4,  CaCl2,  CaCO3 
(amorphous).     Write  all  reactions  concerned. 


CHAPTER   XX 

THE  COPPER-SILVER  GROUP  —  COPPER,  SILVER,  GOLD 

COPPER:  Cu =  63 

1.  History.  —  Copper   has    been   known   from   earliest 
antiquity,  its  use  being  mentioned  by  Jewish,  Assyrian, 
and  other  ancient  historians.     By  the  Greeks  it  was  ob- 
tained  from   the    island   of   Cyprus,    and  from  this  fact 
probably  received  the  name  kuprum,  and  its  present  symbol, 
Cu.     In  England  copper-mining  was  begun  before  the  close 
of  the  twelfth  century.     It  met  with  little  success,  however, 
till  about  five  hundred  years  later.     In  the  United  States, 
the  oldest  mines  are  those  of  the  Lake  Superior  region. 
The  remains  of  prehistoric  tribes  about  the  mines  indicate 
clearly  that  these  deposits  were  known  and  used  in  very 
early  times.     The  metal  was  obtained  by  stripping  the 
rock  and  earth  from  the  outcropping  strata.     When  the 
rock  had  been  broken  or  cracked  off,  the  thin  sheets  of 
copper  were  removed  and  hammered  into  vessels  of  various 
shapes. 

2.  Sources  of  Supply.  —  Besides  the  mines  of  northern 
Michigan,  which  yield  almost  pure  copper,  large  quantities 
are  obtained  from  the  silver  ores  of  Montana  and  Colorado. 
Many  of  the  mines  of  Michigan  are  exceedingly  productive, 
some  of  them  yielding  annually  about  25,000  tons,  but  in 
recent  years  the  mines  of  Montana  have  furnished  about  40 
per  cent  of  the  world's  supply.     Among  the  ores  found  in 
the  Western  mines  may  be  mentioned  malachite,  CuCCX, 
Cu(OH)3,  green  in  color;    azurite,    2  CuCCX,   Cn(OH)2, 

232 


THE  COPPER-SILVER   GROUP  233 

a  beautiful  blue,  usually  associated  with  the  malachite; 
chalcopyrite,  or  copper  pyrite,  CuFeS2,  a  brass-colored 
ore,  resembling  fool's  gold,  but  often  having  a  purplish 
cast ;  and  bornite,  a  sulphide  of  iron  and  copper  of  varying 
proportions,  usually  Cu3FeS3. 

3.  Reduction  of  the  Ore.  —  In  the  case  of  the  copper 
from  the  Lake  Superior  mines,  scarcely  any  refining  is 
necessary.     It  is  passed  through  crushers  to  break  up  the 
rock  associated  with  the  metal,  then  by  washing  and  other 
mechanical  processes  the  separation  is  effected. 

4.  Methods  in  the  West.  —  When  the  ore  is  a  carbonate, 
like  malachite  or  azurite,  or  the  oxide,  it  is  simply  mixed 
with  coke  and  reduced  according  to  the  general  plan  of 
reducing  metallic  ores.     Thus, 

CuO  +  C  =  Cu  +  CO. 

Usually,  however,  there  is  a  high  per  cent  of  sulphur 
present,  and  the  process  is  much  more  complicated.  There 
are,  in  reality,  four  stages  necessary  before  blister  copper, 
that  is  copper  about  98.8  per  cent  pure,  is  obtained.  These 
four  are  concentration,  calcination,  reverberation  or  blast  re- 
duction, and  converting.  The  first  consists  in  the  separation 
of  the  silica  or  rock  from  the  copper  ore.  This  is  done 
by  mechanical  washing  with  "jiggers."  By  calcination 
the  sulphur  is  partially  removed.  After  th~  ore  has  been 
roasted,  either  one  of  two  plans  may  bo  followed.  Accord- 
ing to  one  method,  the  red-hot  ore  is  placed  in  reverbera- 
tory  furnaces  and  melted.  The  sulphide  of  copper,  mixed 
with  the  sulphide  of  iron,  always  present,  and  the  silver 
and  gold,  being  heavy,  settle  to  the  bottom.  This  molten 
mixture  is  drawn  off  and  is  known  as  matte. 

5.  Sometimes  the  ore,  even  without  concentration  or 
calcining,  is  put  directly  into  blast  furnaces.     In  this  case 


234  MODERN  CHEMISTRY 

limestone  rock  is  mixed  with  the  ore  ;  when  the  mass  is 
heated  the  silica  and  limestone  unite  to  form  a  glassy  slag 
which  takes  up  about  75  per  cent  of  the  iron.  The  slag, 
being  relatively  light,  is  drawn  off  above  the  metal.  The 
sulphur  in  excess  is  removed  by  the  strong  draughts 
of  air  which  are  forced  through  the  blast  furnace.  A 
matte  is  thus  obtained  similar  in  composition  to  that  pro- 
duced by  reverberation. 

6.  The  fourth  stage  consists  in  converting  this  matte 
into  blister  copper.      This  is  done  in  a  converter,  which 
in   its   essentials   is   not  unlike   the  Bessemer  converter 
described  in  detail  in  the  chapter  on  iron.     The  molten 
matte  has  fine  streams  of  air  driven  through  it,  and  in 
a  few  minutes  is  converted  into  copper  about  98.5  per 
cent  pure.     This  still  contains  small  quantities   of  iron, 
arsenic,  gold,  and  silver,  which  are  finally  separated  at 
the  refineries. 

EXPERIMENT  138.  —  Put  upon  charcoal  a  little  copper  oxide,  CuO, 
mixed  with  sodium  carbonate,  and  heat  strongly  in  the  reducing  flame. 
Note  the  color  of  the  granular  mass  remaining.  Test  its  malleability 
with  a  hammer.  What  have  you  obtained  ? 

7.  Characteristics  of  Copper.  — Copper  is  a  very  tena- 
cious, malleable,  ductile  metal,  of  a  reddish  color.     It  does 
not  tarnish  in  dry  air,  but  in  the  presence  of  moisture  and 
carbon  dioxide  is  slowly  converted  into  a  green  carbonate 
of  copper.     With  the  exception  of  silver  it  is  the  best 
conductor  of  electricity  known.     Its  melting  point  is  high, 
being  nearly  1100°  C.     In  the  oxidizing  flame  it  is  con- 
verted into  the  black  oxide  of  copper,  CuO.     It  is  soluble 
in  nitric  acid  and   in   hot   concentrated   sulphuric   acid. 
From  its  solutions  it  is  easily  precipitated  by  iron,  zinc, 
and  certain  other  metals. 


THE  COPPER-SILVER  GROUP  235 

8.  Applications  in  the  Arts. — With  the  exception  of 
iron,  copper,  probably,  has  more  varied  uses   than  any 
other  metal.     It  is  employed  very  extensively  in  alloys, 
among  them  being  the  following :  — 

Brass :  consisting  of  copper  and  zinc  in  varying  pro- 
portions. 

Bronze  :  copper,  zinc,  and  tin. 

Bell-metal :  copper  and  tin. 

Coinage  :  gold  and  silver  with  copper. 

Aluminum  bronze  :  aluminum  and  copper. 

A  peculiarity  of  the  last  is  that,  with  about  1  to  3 
per  cent  of  copper,  it  is  of  a  beautiful  silver-white  color, 
much  whiter  even  than  aluminum;  with  10  per  cent  of 
copper  it  somewhat  resembles  gold.  In  the  latter  propor- 
tions it  is  used  largely  for  making  various  fancy  articles 
and  novelties. 

9.  Unalloyed,  copper  is  used  for  roofing,  for  the  sheath- 
ing of  vessels,  for  making  various  utensils,  and  for  wire  for 
trolley,  telegraph,  and  telephone  systems,  and  for  electric 

lighting. 

Compounds  of  Copper 

10.  Two  Classes  of  Salts.  —  Copper,  like  several  other 
metals,  forms  two  classes  of   salts,  cuprous  and  cupric, 
though  as  a  rule  only  the  latter  are  of  importance. 

11.  Cupric  Sulphate,  CuS04,  5  H20.  —  This  is  commonly 
known  as  blue  vitriol.     It  forms  in  beautiful  blue  crystals, 
and  is  obtained  when  metallic  copper  is  dissolved  in  boil- 
ing sulphuric  acid.     The  commercial  supply  is  obtained 
mostly  as  a  by-product  from  the  great  gold  and  silver 
refineries,  such  as  those  of  Kansas  City  and  Omaha.     The 
smelters  at  the  former  place  produce  monthly  about  eight- 
een hundred  tons,  worth  between  $100,000  and  1200,000. 
The  silver  ores  contain  more  or  less  copper  in  the  form  of 


236  MODERN  CHEMISTRY 

cupric  sulphide,  which  in  the  roasting  of  the  ore  is  con* 
verted  into  cupric  sulphate. 

CuS  +  2  O2  =  CuSO4. 

This,  being  soluble  in  water,  is  washed  out  and  concentrated, 
whereupon  the  crystals  separate  out  from  the  solution. 

12.  Characteristics  and  Uses. — The  salt  is  somewhat 
efflorescent,  and  when  exposed  to  the  air  gradually  gives 
up  a  portion  of  its  water  of  crystallization.     At  the  same 
time  it  breaks  up  and  becomes  almost  white  in  color.     By 
heating,  the  water  of  crystallization  may  be  entirely  re- 
moved   and    the    blue    color   destroyed.       This   may    be 
restored,  however,  by  digesting  for  some  time  in  water. 
Blue  vitriol  is  very  poisonous,  and  is  used  extensively  in 
making  Paris  green  and  Bordeaux  mixture  for  spraying 
fruit   trees    to   destroy  moths   and    other  insects.     It   is 
employed  largely  in  electroplating  and  electrotyping,  also 
in  galvanic  batteries,  though  the  dynamo  is  now  taking 
the  place  of  these  batteries. 

13.  Cupric  Nitrate,  Cu(N03)2,  3  H20.  —  This  is  a  deep  blue 
solid,  soluble  in  water,  obtained  when  copper  is  treated 
with  nitric  acid. 

14.  Cupric  Chloride,  CuCl2.  —  This  is  a  beautiful  tur- 
quoise-blue, finely  crystallized  salt. 

15.  Cupric  Sulphide,  CuS.  — This  is  a  black  precipitate 
obtained  when  a  current  of  hydrogen  sulphide  is  passed 
through  a  solution  of  a  copper  salt.     It  is  soluble  in  hot 
nitric  acid,  and  partially  so  in  warm  yellow  ammonium 
sulphide. 

16.  Cupric    Acetylide,    CuC2,  H20,    or    CuC2.  —  Cupric 
acetylide   is  a   reddish   brown   precipitate   formed  when 
acetylene  is  passed  through  a  copper  solution.     In  drying 
it  gives  up  its  molecule  of  water  and  becomes  very  explo- 


THE  COPPER-SILVER   GROUP  237 

sive,  a  slight  jar  being  sufficient  to  touch  it  off.  Metallic 
copper  which  has  for  some  time  been  in  contact  with  moist 
calcium  carbide  is  partially  converted  into  the  acetylide, 
and  shows  the  same  explosive  tendencies. 

17.  Cupric  Oxide,  CuO.  —  This  is  a  black  powder,  ob- 
tained when  copper  is  heated  to  redness  in  the  air,  or 
when  cupric  nitrate  is  treated  in  a  similar  manner.  In 
the  hydrated  form,  CuO,  H2O,  it  may  be  obtained  by 
treating  a  copper  solution  with  caustic  soda  or  potash 
and  boiling  for  a  few  minutes. 

EXPERIMENT  139.  —  To  prepare  some  of  the  above  compounds. 
The  nitrate  and  sulphate  have  already  been  prepared.  Review  the 
work  with  nitrogen  dioxide  and  sulphur  dioxide. 

Add  to  a  few  cubic  centimeters  of  copper  nitrate  solution  a  few 
drops  of  ammonium  sulphide,  (XH4)2S,  or  pass  through  it  a  current 
of  hydrogen  sulphide.  Xote  the  color  of  the  precipitate  formed.  What 
is  it? 

Put  into  a  crucible  or  small  evaporating  dish  a  half  gram  of  pow- 
dered copper  nitrate,  and  heat  gradually  to  dull  redness.  How  is  the 
nitrate  changed ?  What  gas  did  you  see  expelled?  What  have  you 
obtained  ?  Save  the  powder. 

Put  into  a  test-tube  a  few  cubic  centimeters  of  a  solution  of  copper 
nitrate  or  sulphate,  and  add  a  little  caustic  soda  or  potash.  A  blue 
precipitate  of  cupric  hydrate  is  obtained,  Cu(OH)2.  Boil  it  for  a  few 
minutes.  Notice  the  change  in  color.  What  have  you  obtained? 

Make  a  borax  bead  upon  a  platinum  wire  and  fuse  into  it  a  little 
of  the  cupric  oxide  prepared  above.  What  colored  bead  do  you  ob- 
tain ?  The  oxide  is  thus  used  sometimes  in  preparing  emerald  glass. 

EXPERIMENT  140.  Practical  Work.  —  To  determine  the  composi- 
tion of  brass.  Dissolve  a  few  brass  filings  in  warm  nitric  acid.  Notice 
the  color  of  the  solution  obtained.  What  metal  is  indicated  by  the 
color  ?  Evaporate  nearly  to  dryness,  and  take  up  with  40  to  50  cc.  of 
water.  WTarm  gently  and  pass  a  current  of  hydrogen  sulphide  for 
several  minutes,  or  until  no  further  precipitate  will  form.  This  may 
be  determined  by  filtering  out  a  little  and  passing  the  gas  through  it. 
If  no  precipitate  forms,  the  whole  may  be  filtered.  Punch  a  hole  in 
the  bottom  of  the  filter  as  it  rests  in  the  funnel,  and  wash  the  black 


238  MODERN  CHEMISTRY 

precipitate  through  into  a  beaker  with  a  little  nitric  acid  diluted. 
Heat  until  it  dissolves.  What  is  indicated  by  the  color  of  the  solu- 
tion ?  To  prove,  add  ammonia  until  alkaline.  Do  you  obtain  a  deep 
blue  solution?  If  so,  copper  is  indicated. 

The  nitrate  obtained  above  from  the  black  precipitate  will  con- 
tain the  other  metal  or  metals  found  in  the  brass.  Add  to  it  a 
few  drops  of  ammonium  hydroxide  and  then  a  little  ammonium 
sulphide.  Do  you  obtain  a  starchy  white  precipitate  ?  If  so,  zinc  is 
indicated. 

EXERCISE.  —  Write  reactions  showing  the  preparation  of  cupric 
sulphate,  nitrate,  sulphide,  acetylide,  hydrate,  oxide,  and  the  reactions 
in  the  analysis  of  brass  as  far  as  possible. 

SILVER  :  Ag  =  108 

18.  Ores  of  Silver.  —  This  metal  has  been  known  from 
remote  antiquity,  because  of  the  fact  that  it  frequently 
occurs  free  in  small  particles  disseminated  through  quartz 
and  other   rock.     Occasionally  large   masses   have   been 
found,  and  in  the  museum  at  Copenhagen  there  is  to  be 
seen  one  weighing  about  five  hundred  pounds.     Usually, 
however,  silver  is  in  combination  with  other  elements. 
One  of  the  most  important  ores  is  horn  silver,  AgCl,  named 
from  its  general  resemblance  in  color  and  texture  to  the 
horns  of  cattle.     Another  important  ore  is  argentite,  Ag2S. 
As  the  greater  part  of  the  lead  ore  smelted  contains  more 
or  less  silver,  lead  furnaces  yield  the  largest  portion  of 
the  world's  output  of  silver. 

19.  Reduction  of  the  Ores.  — The  following  experiment 
will  illustrate  roughly  one  of  the  methods  by  which  silver 
ores  are  reduced. 

EXPERIMENT  141.  — To  about  10  cc.  of  a  solution  of  silver  nitrate, 
add  a  little  hydrochloric  acid.  The  precipitate  is  silver  chloride, 
AgCl;  shake  the  contents,  warm  slightly,  and  when  the  precipitate 
has  settled,  decant  the  moderately  clear  solution.  Transfer  the  curdy 
white  precipitate  to  a  piece  of  charcoal,  cover  with  sodium  carbonate, 


THE  COPPER-SILVER  GROUP  2S9 

and  heat  strongly  in  the  reducing  flame.  Presently  a  bright  globule 
of  silver  will  appear.  This  may  be  preserved  for  tests  upon  the 
metal  if  desired,  or  dissolved  in  dilute  nitric  acid  and  converted  again 
into  silver  nitrate. 

20.  Other   Methods.  —  Various    processes   are   used  in 
reducing  silver  ores,  depending  upon  the  character  of  the 
ore.     But  so  large  a  proportion  of  the  silver  output  results 
from  lead  reduction,  that  we  shall  confine  ourselves  here 
to  only  one  or  two  of  the  methods  employed.     When  these 
argentiferous  lead  ores  are  reduced  (see  Lead,  page  275), 
the  two  metals,  silver  and  lead,  are  formed  together  as  an 
alloy,  and  they  must  then  be  separated.     There  are  two 
methods  for  doing  this.     When  the  alloy  is  rich  in  silver, 
Pattison's  method  is  employed. 

21.  Pattison's  Method. — It  has  been  found  that  when 
such  an  alloy  is  allowed  to  cool  slowly  the  lead  will  crys- 
tallize before  the  silver.     Hence,  as  the  lead  crystals  begin 
to  form  they  are  skimmed  out  with  perforated  ladles,  thus 
dividing  the  alloy  into  two  portions,  one  containing  the 
silver  with  a  very  little  lead  remaining  in  it,  and  the  other 
the  lead,  with  very  small  quantities  of  silver.     The  first 
of  these  is  then  submitted  to  cupellation.     The  alloy  is 
gradually  run  into  a  large  cupel,  or  basin,  constructed 
upon  a  hearth  within  the  furnace.     A  blast  of  air  and 
flame  is  directed  upon  the  surface  of  the  alloy,  and  the 
lead  is  oxidized  to  litharge,   PbO.     The  current  of  air 
constantly  drives  this  film  of  oxide  off  into  another  vessel 
so  placed  as  to  receive  it.     In  this  way  the  lead  is  entirely 
removed,  and  the  completion  of  the  process  is  known  by 
the  brilliant  appearance  of  the  molten  silver. 

22.  Parke's  Process.  —  Zinc  will  readily  alloy  with  sil- 
ver but  not  with  lead,  and  this  principle  is  made  use  of 
in  Parke's  process  of  separating  lead  and  silver.     Zinc  is 


240  MODERN  CHEMISTRY 

added  to  the  alloy,  and  the  whole  is  melted.  The  alloy  of 
zinc  and  silver,  being  lighter  than  the  lead,  rises  to  the 
surface,  and  as  it  begins  to  solidify  is  skimmed  off  in  the 
form  of  crystals.  "Thus  there  is  obtained  an  alloy  of  zinc 
and  silver  with  very  little  lead  adhering.  This  alloy  is 
now  very  carefully  heated  in  a  -furnace,  the  bottom  of 
which  is  inclined  ;  the  lead  melts  and  runs  off  before  the 
fusing  point  of  the  alloy  is  reached.  The  zinc  still 
remaining  is  next  removed  by  heating  strongly  in  retorts, 
when  it  is  vaporized  and  passes  off. 

EXPERIMENT  142.  —  Making  use  of  the  bead  of  silver  obtained 
above  in  Experiment  141,  test  its  hardness  and  malleability.  Try  to 
oxidize  it  in  the  oxidizing  flame.  Does  any  coating  form  upon  the 
charcoal?  For  just  a  moment  put  a  silver  coin  into  a  solution  of 
hydrogen  sulphide  or  sodium  sulphide.  What  are  the  results?  Next 
immerse  it  in  a  moderately  strong  solution  of  potassium  cyanide,  and 
allow  it  to  remain  some  time,  if  necessary.  State  the  results.  This 
last  suggests  a  method  of  cleaning  tarnished  silverware,  but  it  should 
be  used  with  caution,  as  the  cyanide  is  deadly  poison. 

EXPERIMENT  143.  —  Add  to  2  or  3  cc.  of  silver  nitrate  a  little  hydro- 
chloric acid,  spread  the  white  precipitate  smoothly  upon  a  sheet  of 

paper,  place  upon  it  any  figure  cut 
from  thick  paper,  and  expose  it  to  the 
light.  In  a  few  minutes,  notice  what 
has  happened.  This  illustrates  the 
method  of  printing  from  photographic 

negatives  upon  sensitized  paper. 
Before      Fie.  53.      After  X,,  .  .    ,         , 

Exposure.  Exposure.  The  experiment  may  be  varied,  and 

with  care  and  patience  most  beauti- 
ful prints  may  be  obtained.  Immerse  in  a  solution  of  silver  nitrate  a 
sheet  of  drawing  paper,  and  allow  it  to  dry  in  the  dark.  Next  immerse 
in  a  solution  of  common  salt,  and  again  let  it  dry  in  the  dark.  When 
ready  to  print,  place  upon  this  paper,  thus  sensitized,  an  old  negative, 
or  even  a  fern  leaf  or  any  similar  object,  and  expose  to  bright  sun- 
light, under  a  sheet  of  glass  to  hold  in  place.  Notice  when  a  deep  pur- 
ple is  obtained,  then  immerse  in  a  solution  of  sodium  thiosulphate,  the 
photographer's  "  hypo,"  and  rinse  thoroughly  in  water  several  times. 


THE  COPPER-SILVER   GROUP  24i 

23.  Characteristics  of  Silver.  —  Silver  is  a  white,  lustrous 
metal,  malleable  and   ductile,  an  excellent  conductor  of 
electricity  and   heat,   of   medium  hardness  and   density. 
It  is  quickly  attacked  by  many  sulphur  compounds  and 
by  the  members  'of  the  halogen  group,  although  it  does 
not  tarnish   in  the  air  at  any  temperature.      In  living 
rooms  silverware  is  tarnished  by  the  action  of  the  sulphur 
gases  thrown  off  in  the  combustion  of  coal  or  of  ordinary 
illuminating  gas.      Eggs  and  various  other  articles  of  food 
tarnish  silverware  for  a  similar  reason.     What  is  known 
as  "  oxidized  "  silver  is  really  that  which  has  been  treated 
with  some  compound  of  sulphur,  producing  silver  sulphide 
upon  the  surface. 

24.  Uses  for  Silver.  — Owing  to  its  brilliancy  and  dura- 
bility, silver  has  long  been  used  for  jewelry  and  various 
other  articles  of   ornament.      Alloyed   with   some   other 
metal  to  make  it  harder,  it  is  employed  extensively  in 
coinage ;  is  also  used  in  amalgams  for  dentistry  and  for 
the   backs  of  high  grade  mirrors,  and  for  plating  innu- 
merable articles  of  use  and  ornament. 

Compounds  of  Silver 

25.  There  are  only  a  few  compounds  that  are  of  interest, 
and  but  one  or  two  that  are  of  any  considerable  value. 

26.  Silver  Nitrate,  AgN03. — This  is  important  because 
most  of  the  other  silver  compounds  are  prepared  from  it, 
and  because  it  has  numerous  applications  in  the  arts.     It 
occurs   in   slab-like,    almost   transparent,  white   crystals, 
which  are  soluble  in  water.     It  is  prepared  by  dissolving 
silver  in  nitric  acid.     When  exposed  to  the  light,  espe- 
cially if  in  contact  with  any  organic  matter,  it  turns  dark. 
It  is  used  for  sensitizing  paper  for  photographic  work,  as 
the  principal  ingredient  of  indelible  ink,  and  in  hair  dyes. 


242  MODERN  CHEMISTRY 

In  the  form  of  lunar  caustic,  which  is  simply  crystallized 
silver  nitrate  fused  and  molded  into  sticks,  it  is  used  in 
cauterizing  wounds,  such  as  dog  bites,  for  ulcerated  sore 
throat,  in  removing  warts  and  other  similar  excrescences 
of  the  skin. 

27.  Silver  Chloride,  AgCl. — This  is  prepared  from  a 
solution  of  silver  nitrate  by  adding  to  it  hydrochloric  acid 
or  any  soluble  chloride,  like  common  salt.     It  is  a  white 
precipitate,  curd-like  in  appearance,  especially  when  shaken 
for  a  moment.     It  is  Soluble  in  ammonium  hydroxide,  and 
in  sodium  thiosulphate,  "hypo."     It  is  much  more  sensi- 
tive to  light  than  the  silver  nitrate,  and  hence  for  photo- 
graphic work  the  latter  salt  is  generally  converted  into  the 
chloride,  or  bromide^  which  is  even  more  sensitive.     It  is 
believed  that  the  light  gradually  converts  this  compound 
back  into  metallic  silver,  which  is  insoluble  in  the  "  hypo," 
while  the  unchanged  portions  of  silver  chloride  are  dis- 
solved out  and  the  paper  thus  de-sensitized. 

EXPERIMENT  144.  —  To  about  1  cc.  of  a  solution  of  silver  nitrate 
add  a  few  drops  of  hydrochloric  acid.  Notice  the  appearance  of  the 
precipitate  that  forms.  What  is  it?  Write  the  reaction.  To  a  por- 
tion of  it  add  a  little  ammonium  hydroxide  and  shake  it.  What 
results?  To  another  portion  add  a  solution  of  "hypo"  and  state  the 
results. 

28.  Silver  Chromate,   Ag2Cr04.  —  This   is   a  blood-red 
powder  obtained  as  a  precipitate  when  potassium  chro- 
mate  is  added  to  a  solution  of  silver  nitrate. 

EXPERIMENT  145.  —  Prepare  the  chromate  as  indicated,  and  note 
its  appearance. 

29.  The  formation  of  silver  chloride  and  the  chromate, 
with  their  characteristic  appearance  and  the  ready  solu- 
bility of  the  former  in  ammonia,  serve  to  distinguish  a 
solution  of  silver,  and  may  be  used  as  tests. 


THE  COPPER-SILVER   GROUP  243 

EXERCISE.  —  Write  the  reactions,  showing  the  preparation  of  sil- 
ver nitrate,  silver  chloride,  and  the  chromate;  also  silver  bromide  and 
iodide,  from  silver  nitrate  with  potassium  bromide,  and  with  sodium 
iodide. 

30.  Photography.  —  At  the  present  time  almost  all  young 
people  take  more  or  less  interest  in  this  wonderful  art. 
The  first  experiments  along  this  line  were  made  as  early 
as  1727,  but  they  were  nothing  more  than  what  the  student 
has  done  in  the  first  part  of  Experiment  143,  and  the  print 
soon  disappeared.     From  that  time  to  this  many  different 
plans  have  been  tried,  but  we  can  only  notice  briefly  that 
used  at  present. 

31.  Preparation  of  the  Plates.  —  The  plates  upon  which 
the  negatives  are  made  are  prepared  as  follows :    for  the 
most  sensitive  plates,  potassium   or  ammonium  bromide 
with  gelatin  and  silver  nitrate  added  is  dissolved  in  water 
and  heated  to  boiling.     Thus  the  silver  is  converted  into 
silver  bromide :  — 

KBr  +  AgNO3  =  AgBr  +  KNO3. 

An  excess  of  water  is  added,  and  the  potassium  nitrate 
formed  is  readily  washed  away.  This  gelatin  emulsion, 
as  it  is  known,  is  poured  upon  glass  plates  and  allowed  to 
harden ;  they  are  then  ready  for  use. 

32.  Exposure  and  Developing.  —  As  previously  stated, 
when  such  plates  are  exposed  to  light,  the  silver  salts  are 
decomposed.     In  the  camera  the  exposure  is  so  brief  that 
the  decomposition  is   only  partial;    when,  however,  the 
plate   is   put   into  the  developer ,  this  solution  continues 
the  action  begun  by  the  light.     Hence  those  portions  of 
the  plate  which  have  received  the  most  light  have  the 
larger  amount  of  the  silver  salts  decomposed,  and  are  dark 
in  color.     If  allowed   to  remain  in  the   developer  long 


244  MODERN  CHEMISTRY 

enough,  all  the  silver  would  be  reduced,  and  the  plate 
would  be  uniformly  dark. 

33.  Fixing.  —  When  it  is  seen  by  examination  that  the 
development  has  proceeded  long  enough,  the  plate  is  rinsed 
in  water  and  placed  in  the  fixing  bath.     This  is  a  solution 
containing   sodium   thiosulphate,    which   is   an   excellent 
solvent  for  many  silver  compounds.     The  fixing  bath  soon 
removes  from  the  gelatin  film  the  silver  bromide  or  chlo- 
ride that  remains  unaffected  by  the  light  or  by  the  devel- 
oper.    The  plate  is  thus  cleared  or  fixed,  and  is  no  longer 
sensitive  to  light.      As  the  lights  and   shadows  are  all 
reversed,  it  is  called  a  negative.     After  thorough  washing 
it  is  allowed  to  dry,  when  it  is  ready  to  be  used  in  making 
prints. 

34.  Printing.  —  Various  kinds  of  paper  are  now  used 
for   making  prints,  among   them   being   the  solio,  velox, 
platinotype,  carbon,  and  Hue  print.     The  first  and  last  of 
these  require  the  least  skill.     Solio  has  a  sensitized  film 
of  silver  chloride  ;  in  printing,  this  is  placed  against  the 
film  side  of  the  negative,   which  causes   the   objects  to 
appear  in  the  picture  in  their  natural  position.     As  the 
dark  portions  of  the  negative  transmit  the  fewer  light 
rays,  the  picture  appears  as  a  positive,  or  like  the  original 
as  to  high  lights  and  shadows.     The  advantage  of  solio 
is  in  the  fact  that  it  is  only  moderately  sensitive,  and 
that   it  readily  shows  when  it   has   been   exposed   long 
enough.     More  sensitive  papers,  such  as  the  velox,  are 
like  the  gelatin  plates  in  that  they  show  no  image  until 
treated  with  a  developer.     Solio  prints  require  toning, 
and  all  varieties  need  fixing  by  some  method  or  other. 
In  the  platinotype   papers,  a  compound  of   platinum  is 
used  which  yields   the   dark   appearance   now  so   much 
admired. 


THE  COPPER-SILVER  GROUP  245 

35.  Solio  papers  cost  so  little  that  it  would  be  easy  for 
a  class  to  make  some  experiments  along  this  line.     Let 
any  of  the  pupils  who  may  have  them  bring  in  some  of 
their  negatives  and  printing  frames,  and  do  some  work  of 
this  kind. 

36.  Blue  prints*  are  the  simplest  of  all,  are  cheap,  and 
yet    for    landscapes    often    give    most    excellent    effects. 
They  possess  the  advantage  of  requiring  no  toning  or 
fixing  except  such  as  is  secured  by  thorough  washing. 
Place  the  paper  under  the  negative  in  direct  sunlight, 
and  allow  it  to  remain  until  the  high  lights  begin  to  look 
somewhat  muddy  in  appearance  ;  then  put  into  a  basin  of 
water  with  the  printed  side  down.     Allow  the  print  to 
remain  there  until  the  light  portions  are  quite  clear,  then 
wash  for  ten  minutes  in  running  water.     The  beauty  of 
these  prints  will  be  enhanced  by  leaving  a  pure  white 
border  around  the  picture  ;  this  may  be  secured  by  using 
a  black  mat  between  the  negative  and  print  so  as  to  cover 
the  portion  which  it  is  desired  to  have  white. 


*  If  he  desires,  the  instructor  may  prepare  his  own  blue  print  paper. 
Make 

Solution  A 

Citrate  of  iron  and  ammonia         .        .      1  g. 
Water  .        .        .        .    .    .        .        .    10  cc. 

Solution  B 

Potassium  ferricyanide .        .        .  1  g. 

Water    .        .        .        .        .        .        .     10  cc. 

When  ready  for  use  mix  A  and  B  in  a  dark  room,  and  apply  to  the  paper 
with  a  brush  ;  or,  the  paper  may  be  floated  in  the  solution.  This  must 
be  used  within  a  day  or  two  after  it  is  prepared,  as  it  does  not  keep 
well.  A  few  drops  of  a  10  per  cent  solution  of  potassium  bromide 
added  to  A  and  B  above  will  render  the  keeping  qualities  of  the  paper 
much  better. 


246  MODERN  CHEMISTRY 

GOLD:  Au  =  197 

37.  Occurrence.  —  From  the  fact  that  gold  occurs  free, 
it  has  been  known  from   the   earliest   antiquity.     It   is 
widely  distributed  over  various  portions  of  the  earth  and 
usually  occurs  in  fine  grains  and  nuggets  disseminated 
through  the   rocks.     These   are   gradually  disintegrated 
and  brought  down  by  rains  and  streams  in  the  form  of  sand 
and  gravel,  with  which  the  gold  is  associated.     The  best- 
producing  gold  regions  are  those  of  the  western  part  of 
the   United  States,  Australia,  Southern  Africa,  and  the 
Klondike.     Gold  also  occurs  in  quartz  veins  deeply  buried 
in  the  earth's  strata. 

38.  Methods  of  Mining.  —  The  original  method  consisted 
simply  in  cradling  or  panning  the  sand  and  gravel ;  thus 
the  nuggets  and  larger  grains  find  their  way  to  the  bot- 
tom, while  the  lighter  stone  and  earthy  matter  is  washed 
out.     By  this  method  only  the  larger  particles  are  saved. 
Placer  mining  consists  in  washing  the  gold-bearing  sand 
down  through   sluices,   along  the    bottom   of   which  are 
arranged  pockets  of  mercury,  or  over  plates  of  copper 
amalgamated  with  mercury.     This  readily  amalgamates 
with  the  gold,  and  the  other  portions  are  carried  awTay 
by   the   current.     The   gold   amalgam   thus   obtained   is 
heated   in   retorts,   by  which  the    mercury  is  vaporized, 
leaving  the   gold  behind.     The  vapors  of   mercury  are 
conducted  into  cold  chambers  where  they  are  condensed, 
so  that  very  little  loss  occurs.     Hydraulic  mining  differs 
from  the  above  only  in  that  streams  of  water  are  directed 
with  great  force  against  the  loose  rock  and  cliffs  over- 
hanging, washing  them  down  into  the  sluice-ways. 

39.  Vein  Mining.  —  Vein   mining   differs   from   placer 
mining  in  that  the  latter  is  surface  mining,  while  in  the 


THE  COPPER-SILVER  GROUP  247 

former  the  ore  is  taken  from  greater  or  less  depths,  usually 
from  quartz  veins  ;  hence  it  is  sometimes  called  quartz 
mining.  Gold  sometimes  occurs  in  combination  with 
iron  in  pyrites,  and  it  is  then  obtained  by  the  wet  or 
Morination  process.  The  ore  is  roasted,  then  moistened 
and  treated  with  chlorine,  obtained  usually  from  bleach- 
ing powder.  The  chlorine  dissolves  the  gold,  forming  gold 
chloride,  AuCl3.  This  is  now  dissolved  out  and  ferrous 
sulphate  added,  which  precipitates  gold  in  the  metallic 
condition,  as  seen  in  the  following  reaction  :  - 

6  FeSO4  +  2  AuCl3  =  2  Au  +  2  Fe2(SO4)3  +  Fe2Cl6. 

40.  Cyanide  Process.  —  Potassium  cyanide  is  an  excel- 
lent solvent  for  gold,  and  at  the  present  time  is  used 
extensively  in  separating  it  from  its  ores.     The  process 
is  valuable  where  the  gold  occurs  in  a  finely  divided  form; 
another  advantage  is  that  the  ore  does  not  need  the  roast- 
ing that  is  necessary  in  the  chlorination  process.     After 
the   gold-bearing   quartz   has  been  finely  crushed,  it  is 
treated  with  a  solution  of  potassium  cyanide  in  water. 
The  gold  is  dissolved  out,  thus  :  — 

4  Au  +  8  K(^T+  02  +  2  H20  =  4  KAuCy2  +  4  KOH. 

41.  The  oxygen  shown  in  the  reaction  is  derived  from 
the  air,  and  it  has  been  found  that,  unless  the  surface  of 
the  ore  is  left  well  exposed,  the  process  is  not  satisfactory. 
The  double  cyanide  of  gold  and  potassium  thus  obtained 
is  treated  with  zinc,  which  precipitates  the  gold,  as  shown 
in  the  reaction  :  — 

2  KAuCy2  +  Zn  =  K2ZnCy4  +  2  Au. 

42.  There  is  always  some  zinc  left  in  a  more  or  less 
finely  divided  form  which  cannot  be  separated  mechani- 
cally from  the  gold ;  hence,  when  melted  down  the  metal 


248  MODERN  CHEMISTRY 

is  seldom  over  80  per  cent  pure.  For  this  reason  some 
companies  prefer  to  deposit  the  gold  by  electrolysis  upon 
lead  terminals.  By  this  method,  after  oxidizing  the  lead 
in  cupels,  the  gold  remains  in  a  very  pure  form. 

43.  Characteristics.  —  Gold   is  a  bright   yellow  metal, 
which,  seen  in  light  reflected  several  times,  looks  red.     It 
is  so  soft  that  for  ordinary  purposes  it  must  be  alloyed 
with  some  other  metal ;  it  is  heavy,  is  not  affected  by  the 
oxygen  of  the  air  at  any  temperature,  is  very  ductile  and 
malleable.     Advantage  is  taken  of  this  property  in  ham- 
mering out  the  metal  into  gold  leaf,  the  thickness  of  which 
is  not  over  3-5- oW^  Part  °^  an  incn»  1500  of  which  sheets 
are  necessary  to  make  one  as  thick  as  ordinary  note  paper. 
Pure  gold  is  not  affected  by  single  acids,  but  is  readily 
attacked  by  aqua  regia,  forming   gold  chloride,  AuCl3. 
However,  if  richly  alloyed  with  several  other  metals,  it 
becomes  soluble  in  single  acids. 

44.  Uses.  —  These  are  too  well  known  to  need  specifi- 
cation.    In  the  arts  gold  leaf  has  numerous  uses,  such  as 
in  making  display  signs,  covering  high  grade  moldings, 
for  filling  teeth,  etc. 

SUMMARY   OF   CHAPTER  — COMPARATIVE  STUDY 

Copper,  Silver,  Gold. 

Histories  —  Wherein  are  they  similar? —  Why ? 
Occurrence  —  In  what  forms  ? 
Most  productive  regions. 
Some  important  ores. 

Various  forms  of  gold  mining  —  Description. 
Reduction  of  the  ores. 

Special  plans  for  copper. 

Special  processes  for  gold  reduction. 

Chlorination  and  cyanide. 
Special  plans  for  separation  of  silver. 
Pattison's  and  Parke's. 


THE  COPPER-SILVER  GROUP  249 

Comparison  of  the  three  metals  as  to 

a.  Color. 

b.  Density. 

c.  Melting  point. 

d.  Permanency  in  the  air. 

e.  Malleability. 

f.  Conductivity. 

g.  Solubility  in  acids. 
Uses  of  the  metals. 

a.  Important  alloys. 

b.  Other  uses  —  Why  so  used. 
Compounds  —  Most  important. 

Of  Copper  —  The  Sulphate  —  Commercial  name  and  formula. 

How  obtained. 

Characteristics  and  uses. 
Of  Silver  —  The  Nitrate  —  Commercial  name  and  formula. 

How  prepared. 

Appearance  and  uses  —  Why  so  used  ? 

What  other  compounds  prepared  from  this  one  ?    How  ? 
Special  points. 

Meaning  of   the  terms   blister  copper,   matte,   concentration, 

.  calcination,  converting. 

Describe  method  of  determining  the  composition  of  brass. 
Meaning  of  terms  cupel,  cupellation. 

Describe  experiment  illustrating  principles  of  photography. 
Method  of  sensitizing  photographic  plates. 
Chemistry  of  the  developing  and  fixing  of  negatives. 
Reactions  showing  the  preparation  of  CuSO4,  CuO, 
AgCl,  AgBr,  Agl. 


CHAPTER   XXI 

ZINC,  CADMIUM,  MERCURY 
ZINC  :    Zn  =  Go 

1.  History.  —  Brass,  an  alloy  of  copper  and  zinc,  has 
been  known  for  centuries,  but  it  was  formerly  made  by 
fusing   together   copper   and  a  mineral  called    calamine, 
which  we  now  know  is  an  ore  of  zinc.     It  was  not  until 
about  the  close  of  the  seventeenth  century  that  zinc  was 
recognized  as  a  distinct  metal  and  its  characteristics  care- 
fully determined. 

2.  Ores  of  Zinc.  —  Zinc  occurs  abundantly  in  many  parts 
of  the  United  States  and  Europe.     In  Missouri  the  mines 
of  Joplin   and  Webb   City  are  the  best  known.     There 
thousands  of  tons  are  produced  annually.      Kansas  also 
yields  a  considerable  quantity.     The  ore  most  generally 
found  in  these  states  is  the  sulphide,  ZnS,  known  as  zinc 
blende.      By  the  miners  it  is  called  "jack,"  or  in  its  purer 
forms  "  rosin  jack,"  because  of  the  general  resemblance  of 
a  broken  specimen  of  the  ore  to  rosin.     In  New  Jersey  the 
ore  franklinite  is  the  most  abundant.     It  is  a  mixture  of 
zinc  oxide  and  ferric  oxide,  (ZnFe)Fe2O4.      Other  sections 
yield  the  carbonate,  ZnCO3,  known  as  smithsonite.     It  is 
said  that  the  metal  is  sometimes  found  pure  in  Australia. 

3.  Reduction  of  the  Ores.  —  The  general  method  em- 
ployed in  the  reduction  of  the  greater  number  of  metallic 
ores  is  used  in  the  case  of  zinc.     They  are  first  ground 
fine  aad  roasted.     This  not  only  drives  out  certain  volatile 

250 


ZINC,  CADMIUM,  MEEGUEY  251 

impurities,  such  as  arsenic,  but  converts  the  ore  into  the 
oxide,  ZnO,  the  most  convenient  form  for  the  next  step. 
The  reaction  that  takes  place  when  the  ore  is  roasted  may 
be  seen  from  the  following  :  — 

ZnS  +  3  O  =  ZnO  +  SO2, 
ZnCO3  +  heat  =  ZnO  +  CO2. 

4.  The  oxide  thus  obtained  is  mixed  with  powdered 
coke  and  heated  red  hot  in  earthen  cylinders  about  4J 
feet  long,  placed  horizontally  over  one  another.     The  zinc 
is  thus  reduced  to  the  metallic  form,  and  at  the  tempera- 
ture obtained  is  vaporized.      The  vapors  pass  out  into 
conical-shaped  earthen  condensers  attached  to  the  outer 
end  of  the  retorts,  where  they  liquefy.     Twice  in  twenty- 
four  hours  these  condensers  are  "  tapped  "  and  the  molten 
zinc  drawn  off  and  run  into  molds.     The  chemical  change 
taking  place  is  a  familiar  one  :  — 

ZnO  +  C  =  Zn  +  CO. 

The  retort  is  shown  by  R  in  the  figure  and  the  con- 
denser by  C.  The  condensers  are  readily  detached,  and 
when  the  retorts  have  been  charged  or  filled  with  the 
mixed  ore  and  coke  they  are 
again  attached  and  luted  on 

nearly     air-tight     with      clay. 

^ru  •  4.1  FIG.  54. 

When    in    operation    there    is 

usually  some  escape  of  vaporized  zinc  with  other  gases, 
and  these,  in  burning  at  the  mouth  of  the  condensers, 
give  a  beautiful  display  of  colors,  yellow  and  blue  and 
white,  which,  especially  at  night,  is  exceedingly  striking. 

5.  A  single  charge  requires  about  twenty-four  hours 
for  complete  reduction,  and  as  the  workmen  are  usually 
paid  by  the  amount  of  metal  they  "  draw  off  "  they  gen- 


252  MODERN  CHEMISTRY  _ 

erally  work  twenty-four  hours  successively,  and  then  are 
off  during  the  next  twenty-four.  The  zinc  obtained  in 
this  way  is  more  or  less  impure ;  it  almost  always  contains 
some  cadmium,  and  usually  some  arsenic,  and  is  known 
as  "  spelter." 

6.  Characteristics  of    Zinc.  —  Zinc   is   a   bluish   white 
metal  of  moderately  low  melting  point,  about  420°  C. ;  it 
tarnishes  but  slightly  in  the  air,  and  then  only  upon  the 
surface.      At  a  temperature  slightly  above  the  melting 
point  it  burns  with  a  brilliant,  bluish  white  flame,  and  if 
a  jet  of  oxygen  be  directed  upon  it  the  light  is  almost 
dazzling. 

EXPERIMENT  146. —  Examine  a  piece  of  zinc  and  note  its  color, 
malleability,  hardness,  and  tendency  to  oxidize.  Test  also  its  melting 
point  by  heating  a  small  piece  on  charcoal  with  the  blowpipe.  Try 
it  also  with,  the  oxidizing  flame  and  note  the  deposit  upon  the  char- 
coal, both  when  hot  and  when  cold.  State  the  results. 

EXPERIMENT  147.  —  To  learn  the  solvents  for  zinc.  Try  a  small 
piece  of  the  metal  in  a  test-tube  with  hydrochloric  acid.  How  is  it 
affected?  What  gas  is  obtained?  What  proof  can  you  offer?  Write 
the  reaction. 

In  the  same  way  try  nitric  acid,  and  compare  results  with  the 
above. 

Into  each  of  two  test-tubes  put  a  small  piece  of  zinc.  To  one  add 
about  a  cubic  centimeter  of  copper  sulphate  solution,  and  cover  the 
other  with  water.  After  a  few  moments,  to  each  add  a  little  sulphuric 
acid.  Is  there  any  difference  in  the  rapidity  of  the  chemical  action  in 
the  two  cases?  Why? 

EXPERIMENT  148.  —  Sift  some  zinc  dust  through  a  wire  sieve  of 
fine  mesh  upon  a  Bunsen  burner  flame  and  note  the  results. 

7.  Further    Characteristics    of    Zinc.  —  Ordinary  com- 
mercial zinc  as  it  comes  from  the  smelter  is  brittle,  but  if 
it  is  heated  to  something  over  120°,  and  then  rolled  into 
sheets  or  drawn  into  wires,  it  is  found  to  be  malleable,  and 
will  remain  so.     As  it  approaches  the  melting  point,  how- 


ZINC,   CADMIUM,  MEECUET  253 

ever,  it  again  becomes  brittle,  and  may  be  ground  into  a 
powder  known  as  zinc  dust.  It  is  of  medium  density, 
being  a  little  lighter  than  iron,  is  not  magnetic,  and  when 
chemically  pure  is  but  slightly  soluble  in  dilute  acids. 
When  impure,  or  if  in  contact  with  some  other  metal,  as 
copper  or  platinum,  the  solution  is  rapid. 

8.  Uses  for  Zinc.  —  In  the  metallic  form  zinc  is  used 
extensively  in  many  varieties  of  galvanic  batteries,  also  as 
linings  for  refrigerators,  bathtubs,  and  for  various  other 
domestic  purposes.     One  of  its  most  important  applica- 
tions is  in  coating  or  "  galvanizing  "  iron  wire  and  other 
forms  of  iron  as  a  protection  from  moisture.     Galvanized 
iron  is  prepared  by  thoroughly  cleansing  the  iron  to  be 
coated,  heating  it,  and  plunging  it  into  a  bath  of  molten 
zinc  until  a  thin  covering  of  the  latter  metal  adheres. 
There  are  also  three  important  alloys  :  — 

Brass :  consisting  of  zinc  and  copper  in  varying  propor- 
tions ; 

Bronze  :  zinc,  copper,  and  tin  ; 

German  silver  :  zinc,  copper,  and  nickel. 
In  the  chemical  laboratory  zinc  is  frequently  used  :    in 
making  hydrogen ;  in  reducing  ferric  compounds  to  the  fer- 
rous condition  ;  and  for  precipitating  various  metals  from 

their  solutions. 

Compounds  of  Zinc 

9.  Zinc  Sulphate,  ZnS04,  7  H20.  —White  Vitriol.  —This 
is  a  white  crystalline  salt  which  has  been  obtained  in  the 
preparation  of  hydrogen  by  treating  zinc  with  sulphuric 
acid.     It  is  very  soluble  in  water,  and  is  used  mainly  for 
calico  printing.     It  has  a  bitter,  astringent  taste. 

10.  Zinc  Chloride,  ZnCLj.  —  This  is  a  white  solid,  ob- 
tained when  zinc  is  dissolved  in  hydrochloric  acid.  It  has 
great  affinity  for  water,  and  is,  therefore,  often  used  in 


254  MODERN   CHEMISTRY  ' 

chemistry  as  a  drying  agent.  It  is  also  frequently  used  as 
a  soldering  solution,  but  as  it  is  poisonous,  serious  results 
have  sometimes  followed  its  use  in  soldering  tin  cans  con- 
taining fruits  and  other  food  products. 

11.  Zinc  Hydroxide,  Zn(OH)2.  — This  compound  of  zinc 
may  be  studied  in  the  following  experiment :  — 

EXPERIMENT  149.  —  To  a  few  cubic  centimeters  of  a  solution  of 
any  zinc  salt,  as  the  chloride  or  sulphate,  add  a  few  drops  of  ammo- 
nium hydroxide.  What  are  the  results?  Add  more  ammonia;  does 
the  precipitate  dissolve?  Describe  the  precipitate,  Zn(OH)2,  that 
formed,  and  write  reaction.  In  the  same  way  prepare  a  little  zinc 
hydroxide  by  using  a  solution  of  caustic  soda  or  potash  instead  of  am- 
monia as  above.  Test  a  portion  of  the  precipitate  with  hydrochloric 
acid  ;  does  it  dissolve  ?  Write  the  reaction. 

12.  Zinc  Sulphide,  ZnS.  —  Many  characteristics  of  zinc 
sulphide  may  be  discovered  from  the  following  experi- 
ment : 

EXPERIMENT  150.  —  To  a  few  cubic  centimeters  of  a  solution  of 
some  zinc  salt  add  two  or  three  drops  of  ammonium  sulphide.  De- 
scribe the  precipitate  that  forms.  It  is  zinc  sulphide.  Test  its  solu- 
bility in  dilute  hydrochloric  or  nitric  acid. 

13.  Zinc  Oxide,  ZnO.     Zinc  White.  —  This  was  the  white 
deposit  formed  on  charcoal  when  the  zinc  was  heated  by 
the  oxidizing  flame.     It  is  now  used  extensively  as  a  sub- 
stitute for  white  lead  in  painting,  and  is  preferable  in 
localities  where  much  coal  is  used  as  fuel,  because  of  the 
discoloration  of  lead  compounds  by  the  considerable  quan- 
tities of  Hydrogen  sulphide  found  in  coal  smoke. 

*  CADMIUM,  Cd  =  112 

14.  Supply.  —  Cadmium  is  a  rare  element,  discovered 
about  1817.     It  received  its  name  from  a  Greek  word,, 

*  This  is  an  unimportant  element,  and  its  study  may  be  omitted,  if 
desired. 


ZINC,   CADMIUM,  MERCtTRT  255 

kadmeia,  an  ore  of  zinc,  now  known  as  calamine,  with 
which  cadmium  is  usually  associated.  Our  present  supply 
is  obtained  mostly  from  zinc  ores,  with  which  it  is  found, 
in  the  form  of  a  sulphide,  CdS,  called  greenockite. 

15.  Reduction  of  the  Ore.  —  In  smelting  cadmium-bear- 
ing zinc  ores,  they  are  first  roasted  in  retorts,  where  both 
sulphides  are  converted  into  oxides,  thus  :  — 


These  oxides  are  then  mixed  with  coke  or  charcoal  and 
again  heated,  when  the  usual  reduction  takes  place  :  — 


= 
ZnOJ  IZn 

To  separate  the  two  metals  thus  obtained  they  are  dis- 
solved in  hydrochloric  acid,  and  the  solution  treated  with 
rods  of  zinc,  by  which  the  cadmium  is  reduced  to  the 
metallic  form,  thus  :  — 


and 

+  Zn  =  Cd  +  2  ZnCl2. 


16.  Appearance  and  Characteristics.  —  Cadmium  is  usu- 
ally marketed  in  the  form  of  small  rods,  8  or  10  inches 
in  length.  It  is  a  white  metal,  closely  resembling  tin,  and 
is  of  about  the  same  hardness,  but  it  has  a  melting  point 
not  very  different  from  lead,  315°,  and  boils  at  860°. 
Cadmium  tarnishes  slowly  in  the  air,  becoming  coated 
with  a  very  thin  covering  of  yellow  oxide.  It  is  malleable 
and  ductile,  and  when  bent,  like  tin,  gives  a  creaking  sound. 
With  mercury  it  forms  a  silvery  white  amalgam  which 


256  MODERN  CHEMISTRY 

soon  becomes  hard  and  brittle.  It  is  easily  soluble  in 
nitric  acid,  less  so  in  hydrochloric  and  sulphuric  acids.  It 
is  but  little  used  in  the  arts,  though  it  has  been  applied 
somewhat  as  a  filling  for  teeth ;  but  as  a  cadmium  amal- 
gam gradually  turns  dark,  it  has  not  found  favor  with 
dentists. 

Compounds  of  Cadmium 

17.  Cadmium  Nitrate,  Cd(N03)2.  —  This  is  a  white  salt 
obtained  when  the  metal  is  dissolved  in  nitric  acid. 

18.  Cadmium  Sulphide,  CdS.  —  This  is  a  yellow  powder 
used  in  oil  and  water  colors.     Artificially,  it  is  obtained 
when  a  current  of  hydrogen  sulphide  is  passed  through  a 
solution  of  any  cadmium  salt.     It  resembles  the  sulphides 
of  arsenic  and  tin,  As2S8  and  SnS2.     Unlike  the  arsenic, 
however,  cadmium  sulphide  is  not  soluble  in  ammonium 
carbonate,  and  unlike  the  tin,  is  insoluble  in  yellow  ammo- 
nium sulphide. 

EXERCISE.  —  Write  reactions  showing  the  formation  of  cadmium 
nitrate,  chloride,  sulphate,  and  sulphide. 

I        ) 

MERCURY:   Hg  =  200 

\*  \  / 

19.  Historical  Facts.  —  Mercury  was  one  of  the  seven 
elements  known  to  ancient  chemists,  and  by  them  was 
dedicated  to  the  god  from  which  it  received  its  name.     Its 
symbol  is  taken  from  the  Greek  word,  hydrargyrum,  by 
which  name  it  was  also  known.     This  term  means  water 
(or  liquid)  silver.      Similarly,  at  the  present  time  it  is 
spoken  of  as  quicksilver.     By  Geber,  the  famous  alchemist 
of  the  eighth  century,  mercury  and  sulphur  were  regarded 
as  the  two  elements  from  which  all  metals  could  be  made. 
He  claimed  that  any  one  knowing  the  proper  proportions 
could  prepare  any  of  the  noble  metals  from  these  two. 


ZINC,   CADMIUM,  MERCURY 


257 


20.  The  Source  of  Supply.  —  The  commercial  supply  of 
mercury  comes  from  its  chief  ore,  cinnabar,  or  vermilion, 
HgS.     This  is  an  exceedingly  heavy,  brick-red  mineral, 
found  in  Spain,  India,  Bavaria,  California,  Mexico,  etc. 

EXPERIMENT  151.  —  Near  one  end  of  a  piece  of  hard  glass  tubing 
place  a  little  vermilion,  HgS,  as  much  as  will  remain  on  the  point  of  a 
knife-blade.  Now,  with  this  end  down,  hold  in  a  slanting  position  in 
the  Bunsen  burner  and  heat  strongly.  Notice  the  formation  on  the 
upper,  cooler  portion  of  the  tube.  What  gas,  detected  by  its  odor,  is 
given  off  from  the  upper  end  of  the  tube  ?  Name  the  two  products 
resulting  from  the  heating  of  mercuric  sulphide.  Compare  with  the 
preparation  of  oxygen  from  mercuric  oxide. 

21.  Reduction  of  the  Ore.  —  This  experiment  illustrates 
the  reduction  of  cinnabar  in  the  preparation  of  mercury 
for  commerce.     The  ore  is  placed 

upon  shelves  in  an  oven  over  a 
furnace  (see  Fig.  55).  Hot  blasts 
of  air  flow  up  through  the  shelves, 
oxidizing  the  sulphur  to  sulphur 
dioxide,  and  at  the  same  time 
vaporizing  the  mercury.  These 

gases  pass  out  together  into  cool  chambers,  where  the  mer- 
cury condenses,  while  the  sulphur  dioxide  escapes.  As 
thus  obtained  the  mercury  is  more  or  less  impure.  It  is 
purified  first  by  being  strained  through  porous  leather  or 
chamois  skin,  and  then  distilled  at  moderate  temperatures. 

22.  Characteristics.  —  Mercury  is  the  only  metal  that  is 
liquid  at  ordinary  temperatures.      At  39°  below  zero  it 
becomes   a   solid,  and  in  that  condition   possesses  some 
of  the  properties  of  lead.     It  has  about  the  same  color,  is 
malleable,  and  soft  enough  to  be  cut  easily.     Mercury  is 
a  silver- white  metal,  which  does  not  tarnish  in  the  air,  but 
which  slowly  vaporizes  at  all  temperatures. 


258  MODERN  CHEMISTRY 

23.  Amalgams. — The    most    remarkable    property   of 
mercury  is  its  power  of  dissolving  many  of  the  metals 
and  forming  with  them  what  are  known  as  amalgams. 
If  the  mercury  be  largely  in  excess,  the  other  metal  dis- 
appears as  a  lump  of  sugar  does  in  a  cup  of  tea  ;  if  a 
smaller  proportion  be  used,  the  mercury  simply  combines 
with  the  outer  portions  of  the  other  metal,  changing  more 
or  less  its  appearance  and  general  properties.     There  are 
two  methods  of  forming  amalgams. 

24.  a.  By  bringing  metallic  mercury  into  contact  with 
a  metal  perfectly  clean.     If  this  is  broken  up  into  small 
pieces,  or  in  the  form  of  dust  or  filings,  and  is  then  heated 
with  the  mercury,  the  amalgamation  takes  place  quickly. 

EXPERIMENT  152.  —  Into  a  few  drops  of  mercury  in  an  evaporating 
dish,  put  a  perfectly  clean  strip  of  zinc.  After  a  few  moments,  ex- 
amine it;  has  it  changed  in  appearance?  Bend  it;  has  it  changed  in 
properties?  Try  in  the  same  way  a  five-cent  piece,  a  penny,  a  nail,  or 
any  other  convenient  metals.  Be  careful,  however,  "of  any  gold  rings, 
as  mercury  amalgamates  very  readily  with  gold. 

25.  b.  The  second  general  method  is  by  immersing  the 
metal  to  be  amalgamated  in  a  solution  of  some  salt  of 
mercury.     Try  in  this  way  the  following :  — 

EXPERIMENT  153.  —  Put  into  a  beaker,  or  evaporating  dish,  a  few 
cubic  centimeters  of  a  solution  of  mercurous  nitrate,  Hg2(NO3).>. 
Immerse  in  it  a  brass  pin,  or  a  thimble,  a  copper  penny,  a  key  ring, 
etc.  After  remaining  a  few  minutes,  they  may  be  removed  and 
rubbed  a  little,  if  dull  in  appearance.  State  which  have  been 
amalgamated. 

26.  This   second   method   is   employed   frequently   by 
street  fakirs  as  a  means  of  "  silver  plating."     They  pre- 
pare the  solution  by  dissolving  mercury  in  nitric  acid 
and  then  adding  some  coloring  matter.    This  very  rapidly 


ZINC,    CADMIUM,  MEECUET  259 

-X-— - — 

"  plates "   certain  metals,  but  the  amalgamated  Articles 
retain  their  brilliancy  but  a  short  time. 

27.  Solvents  for  Mercury.  —  The  best  solvent  for  mer- 
cury is  nitric  acid,  which  attacks  the  metal  even  at  or- 
dinary temperatures.     When  heated,  sulphuric  acid  also 
dissolves  it,  with  the  formation  of  sulphur  dioxide  gas. 
Compare  this  with  the  preparation  of  sulphur  dioxide  as 
given  on  page  177,  section  15. 

28.  Uses  for  Mercury. — Mercury  is  employed  exten- 
sively in  the  manufacture  of  thermometers  and  barom- 
eters ;    in   the    laboratory    it    is    often    used   instead   of 
water  in  the  pneumatic  trough  for  collecting  such  gases 
as  are  soluble  in  water,  especially  when  they  are  desired 
perfectly  free  of  air.     Large  quantities  are  also  used  in 
placer  mining  of  gold  and  silver  (see  page  246).     In  the 
form  of  amalgams  it  is  used  with  various  other  metals  for 
filling  teeth  ;  with  tin  or  silver  for  the  backs  of  mirrors, 
for  rendering  zinc  plates  to  be  used  in  batteries  less  solu- 
ble in  acids,  and  sometimes  for  amalgamating  surfaces 
which  are  to  be  silver  plated.     This  is  done  because  silver 
seems  to  adhere  better  to  a  surface  which  has  been  thus 

treated. 

Compounds  of  Mercury 

29.  Like  several  other  metals,  mercury  forms  two  series 
of  compounds,  the  mercurous  and  mercuric. 

30.  The  Nitrates,  Mercurous,   Hg2   (N03)2 ;    Mercuric, 
Hg(N03)2.  — These  may  be  prepared  by  treating  mercury 
with  nitric  acid  ;  for  the  former,  using  dilute  acid  with 
the  mercury  in  excess ;  for  the  latter,  concentrated,  with 
the  acid  in  excess.     Mercuric  nitrate  is  a  white  salt  of  fine 
silky  crystals,  soluble  in  water.     In  dissolving  it  yields  at 
the  same  time  a  yellowish  powder,  known  as  basic  nitrate, 
having  the  formula  HgNO3,  Hg(OH)3.     Mercurous  ni- 


260  MODERN  CHEMISTRY 

trate  is  of  a  pale  yellow  color,  almost  white.  It  usually 
occurs  in  crystals  larger  than  those  of  the  mercuric  nitrate 
and  is  soluble  in  water.  Both  are  used  in  the  laboratory, 
and  occasionally  for  the  preparation  of  other  compounds 
of  mercury. 

31.  The  Chlorides,  Mercurous,  Hg2Cl2 ;  Mercuric,  HgCl2. 
—  The  former  is  known  as  calomel,  the  latter  as  corrosive 
sublimate.     Mercurous  chloride  may  be  prepared  by  add- 
ing to  mercurous  nitrate,  hydrochloric  acid,  whereupon  it 
falls  as  a  heavy  white  precipitate.     On  a  large  scale  it  is 
manufactured  by  thoroughly  mixing  in  the  proper  propor- 
tions mercuric  chloride  and  mercury,  heating  them  strongly 
to  vaporize,  whereupon  they  combine  and  are  condensed  in 
cold  chambers.     Calomel  is  a  white,  flour-like  substance, 
insoluble  in  water.     It  is  used  largely  in  medicine. 

32.  Mercuric  chloride  is  prepared  by  subliming,  as  de- 
scribed above  in  making  calomel,  a  mixture  of  mercuric 
sulphate  and  common  salt.     It  is  a  white,  crystalline  salt, 
somewhat  soluble  in  water,  and  very  poisonous.     It  is  used 
in  the  laboratory  as  a  reagent,  is  a  constituent  of  some 
vermin  exterminators,  and  has  frequent  use  in  surgery  as 
an  antiseptic. 

33.  Mercuric  Oxide,  HgO.  —  This  orange-red  salt,  com- 
monly known  as  red  precipitate,  is  prepared  by  heating 
mercuric  nitrate  for  a  considerable  length  of  time.     It  is 
used  sometimes  for  preparing  small  quantities  of  oxygen, 
and  in  some  quantitative  determinations  in  the  laboratory. 

34.  Mercuric  Sulphide,  HgS.  —  As  an  ore  it  is  known  as 
cinnabar,  but  the  artificial  product  is  sold  under  the  name 
vermilion.      It  is  of  a  bright  scarlet  color,  and  is  used 
in  making  tube  paints  and  in  coloring  sealing-wax.     As 
ordinarily  prepared  in  the  laboratory,  it  is  black,  but  under 
certain  conditions  is  obtained  in  varying  shades  of  red. 


ZINC,   CADMIUM,   MEECURY 


261 


EXPERIMENT  154.  —  To  prepare  certain  compounds  of  mercury.  Put 
a  drop  of  mercury  into  a  test-tube  and  add  about  a  cubic  centimeter  of 
dilute  nitric  acid,  warm  gently,  and  after  a  few  minutes,  or  when  the 
action  has  ceased,  decant  the  solution ^and  boil  it  nearly  dry  in  an 
evaporating  dish.  Now  add  a  few  cubic  centimeters  of  water  and  pour 
into  three  test-tubes.  To  the  first  add  a  little  potassium  iodide ;  to  the 
second,  hydrochloric  acid ;  to  the  third,  ammonia.  Notice  the  color  of 
the  precipitate  in  each  case.  Write  the  reactions  in  the  first  two,  and 
state  what  compound  is  formed.  Tabulate  results  as  follows :  — 


Hg2(N03)2 


Hg(N03)2 


KI 


HC1 


NH4OH 


q^L 


You  should  have  prepared  mercurous  nitrate  by  the  above  treat- 
ment of  mercury  with  nitric  acid. 

To  another  drop  of  mercury  in  a  test-tube  add  some  strong  nitric 
acid,  and  warm  until  the  mercury  is  all  dissolved.  Transfer  to  an 
evaporating  dish,  boil  nearly  dry,  and  add  a  few  cubic  centimeters  of 
water.  You  should  now  have  a  solution  of  mercuric  nitrate.  Divide 
into  three  parts  and  treat  with  the  same  three  reagents  that  you  used 

with  the  mercurous  nitrate,  and  tabulate  the  results. 

*» 

35.  From  the  above  experiments,  it  will  be  seen  that 
the  two  series  of  mercury  salts  may  be  easily  distinguished 
by  the  precipitates  which  they  form  with  different  reagents. 

EXPERIMENT  155.  —  Let  the  student  be  given  some  mercurous~ahd 
mercuric  solutions,  and  have  him  determine  what  each  is. 

EXERCISE.  —  Write  out  the  reactions  that  take  place  in  preparing 
the  two  nitrates,  mercurous  chloride,  mercurous  and  mercuric  iodide, 


262  MODERN  CHEMISTRY 

and  mercuric  sulphate.  Before  attempting  the  last,  unless  you  know 
the  results,  put  into  a  test-tube  a  small  drop  of  mercury,  add  a  little 
strong  sulphuric  acid,  and  heat  until  some  familiar  gas  is  produced. 

COMPARATIVE  STUDY 

Zinc  and  Mercury  —  Early  history. 

Ores  of  these  metals  —  Most  important  of  each  —  Localities  where 

found. 
Plan  of  reduction. 

Wherein  are  they  alike? 

How  different? 

Why  is  carbon  not  necessary  for  the  mercury? 

Reactions  for  each. 

Description  of  furnaces. 
Comparison  of  the  two  metals  in 

a.  Color. 

b.  Melting  point. 

c.  Density. 

d.  Ease  of  oxidation. 

e.  Malleability. 
/.   Conductivity. 
g.   Solubility. 

Special  properties  of  each. 

Brittleness  of  zinc  at  certain  temperatures. 
Condition  of  -mercury  at  low  temperatures. 
Power  of  forming  amalgams. 

Names  of  metals  which  will  amalgamate  and  of  those 

which  will  not. 

Two  methods  of  making  amalgams. 
Important  uses  of  each  metal. 
Alloys  of  zinc. 
Amalgams  of  mercury. 
Other  uses. 
Compounds. 

The  oxides  —  Appearance  and  use  of  each. 
The  chlorides  —  One  of  zinc,  two  of  mercury. 

Preparation  of  each  —  Use  —  Commercial  name. 
Two  classes   of   mercury  compounds  —  Methods   of  distin- 
guishing them. 


CHAPTER   XXII 

ALUMINUM  AND  ITS  COMPOUNDS 

ALUMINUM  :  Al  =  27 

1.  Abundance.  —  This   metal    was   first   isolated   about 
1827,   being    reduced    by    metallic    sodium.       For    some 
years  all  that  was  used  in  the  arts  was  prepared  by  strongly 
heating  aluminum  chloride,  and  passing  the  vapors  into 
which  it  was  converted  over  sodium.     The  reaction  may 
be  represented^  us :  — 

AlClg  4  3  Na  =  Al  +  3  NaCl. 

By  this  method  about  three  pounds  of  sodium  were  re- 
quired for  the  preparation  of  a  single  pound  of  aluminum, 
and  the  cost  was  about  one  dollar  an  ounce. 

2.  No  metal  occurs  more  abundantly  than  aluminum, 
and  but  one  or  two  non-metallic  elements  are  more  widely 
distributed.     It  forms  a  large  per  cent  of  feldspar  and  of 
various  other  ro<?ks,  and  consequently,  from  their  decom- 
position, of  all  clays. 

3.  The  Commercial  Supply.  —  It  is  evident  that  all  that 
is  needed  to  insure  a  large  output  of  aluminum  is  a  cheap 
process  of  reducing  it  from  its  natural  compounds.    Various 
methods  have  been  patented,  but  none  has,  as  yet,  brought 
aluminum  within  the  reach  of  all,   although  its  market 
value  now  is  only  about  $1.50  per  pound.     Perhaps  the 
most  satisfactory  plan  yet  adopted  is  the  following :  a  is  a 
large  crucible  lined  with  some  infusible  substance,  like 

263 


264  MODERN  CHEMISTRY 

graphite;    c  is  a  bundle  of  carbon  rods.      The  crucible 
and  carbons  are  made  the  kathode  and  anode  from  the 

dynamo  d.  Into  the  crucible 
is  put  cryolite,  a  compound  of 
aluminum  and  sodium  fluor- 
ide, Na3AlF6,  mixed  with 
bauxite,  i.e.,  aluminum  oxide, 
A12O3.  The  former  compound 
has  a  very  low  melting  point 
FIG  56  and  serves  as  a  flux.  When 

the  mixture  of  the  two  min- 
erals has  been  fused,  a  powerful  current  is  passed  through, 
and  the  bauxite  alone  is  decomposed.  We  may  represent 
this  by  the  simple  equation 

A12O3  =  A12  +  3  O. 

The   metallic   aluminum   collects   at   the   bottom  of   the 
crucible  and  may  be  drawn  off. 

4.  Characteristics.  —  Aluminum  is  a  silvery  white  metal, 
having  a  density  of  only  2.6,  or  about  one-third  that  of 
iron.     It  is  very  tenacious,  ductile,  malleable,  and  sonorous. 
Its  melting  point  is  only  moderately  high,  700°.     It  is 
permanent  in  the  air  and  a  good  conductor  of  electricity. 
Aluminum  is  strongly  electropositive  in  its  character,  and 
may  be  used  to  reduce  various  other  metals  from  their 
compounds,  just  as  zinc  will  reduce  lead,  tin,  and  others. 

5.  Uses. — As  the  output  of  aluminum  has  increased 
and   the   price    cheapened,  its  uses   have    rapidly  multi- 
plied. 

6.  The  metal  will  take  a  very  high  polish,  and  as  it  is 
permanent  in  air  it  is  now  used  extensively  in  the  manu- 
facture of  ornaments  and  novelties,  for  which,  in  the  past, 
silver  alone  had  been  employed. 


ALUMINUM  AND  ITS  COMPOUNDS  265 

7.  A  more  valuable  use  of  aluminum  is  in  the  place  of 
copper  in  electric  circuits.     Because  of  its  lightness,  an 
aluminum  wire,  much   larger   in  cross-section  than  any 
copper  wire  used  for  this  purpose,  may  be  employed  with- 
out increasing  the  weight  in  a  given  length.     This  fact 
will  nearly  suffice  to  offset  the  lower  coefficient  of  conduc- 
tivity of  the  newer  metal,  and  makes  its  carrying  capacity 
not  very  different  from  that  of  copper.     Another  practical 
use  of  aluminum  is  in  the  manufacture  of  cooking  utensils. 
It  is  claimed  that  these  vessels  will  prevent  the  scorching 
of  liquid  foods,  such  as  milk.     The  metal  is  also  used  in 
many  places  where  iron  has  heretofore  been  employed, 
having  the  advantage  of  great  tenacity.     In  time,  if  the 
cost  of  production  is  sufficiently  decreased,  it  may  find 
extensive  use  in  shipbuilding.     In   the   form   of   alloys, 
with  varying  proportions  of  copper,  it  is  much  used. 

Compounds  of  Aluminum  —  Native 

8.  Kaolin.  —This  is  one  of  the  most  valuable  natural 
compounds  of  aluminum  ;    it  is  the  silicate,  H4Al2Si2O9, 
almost  pure.     Ordinary  clays  contain,  in  addition  to  this, 
iron   compounds  and  other  foreign   materials.       Kaolin, 
when  heated  with  a  kind  of  rock  called  feldspar,  melts 
and  forms  a  semi-translucent  mass,  used  in  making  various 
kinds  of  porcelain  wares. 

9.  Emery.  —  In  the  form  of  a  rock  or  mineral,  emery  is 
known  as  corundum.     It  is  the  oxide  of  aluminum,  A12O3, 
and  is  extremely  hard.     It  is  used  in  the  form  of  emery 
wheels,  and  in  other  ways,  for  polishing  and  for  grinding 
and  sharpening  tools. 

10.  Precious  Stones.  —  The  Oriental  ruby,  the  emerald, 
sapphire,  and  many  other  stones  prized  for  their  beauty 
are  merely  aluminum  oxide,  A13O3,  crystallized  with  some 


266  MODERN  CHEMISTRY 

silica,  SiO2,  and  differ  in  almost  no  other  respect  from 
emery  or  corundum,  which  is  uncrystallized.  These  jewels 
contain  in  addition  very  small  quantities  of  some  foreign 
substance,  such  as  iron,  chromium,  or  copper,  which  im- 
parts the  colors  for  which  they  are  valued.  The  true 
or  Oriental  ruby  and  other  gems  differ  from  the  spinel 
or  ordinary  ruby  and  emerald  in  that  the  latter  contain  in 
addition  to  the  aluminum  oxide,  certain  other  compounds, 
which  render  the  stones  much  less  valuable. 

Compounds  of  Aluminum  —  Artificial 

11.  Alums.  —  The  term  alum  is  applied  to  a  large  num- 
ber of  salts,  known  as  double  sulphates.     They  all  contain 
two  metals,  or  an  equivalent.     Thus,  common  alum  is 
potassium  aluminum  sulphate,  K2A12(SO4)4  24  H2O.     By 
inspection,  it  will  be  seen  that  this  is  simply  potassium 
sulphate,    K2SO4,    crystallized   with   aluminum   sulphate, 
A12(SO4)3.     They  all   crystallize   in   octahedrons,  some- 
times   singly,   more   usually   piled   in   masses    one   upon 
another. 

EXPERIMENT  156.  —  Put  about  50  cc.  of  water  into  a  beaker,  warm 
it  somewhat,  and  add  powdered  alum  as  long  as  any  will  dissolve. 
Now,  pour  the  saturated  solution  into  a  good-sized  test-tube,  and  sus- 
pend therein  a  string  with  a  small  knot  at  the  end.  Allow  it  to  stand 
several  hours  and  note  the  shape  of  the  crystals  that  form.  By  adding 
a  strong  chromium  solution  to  the  alum,  delicately  colored  violet  crys- 
tals may  be  obtained. 

12.  Common  alum  is  prepared  by  burning  a  shaly  rock 
which  contains  a  compound  of  aluminum,  moistening  it, 
and  exposing  it  to  the  air.   .  The  aluminum  compound  is 
thus  converted  into  a  sulphate.     A  potassium  salt  is  then 
added  to  the  solution,  whereupon  the  alum  crystallizes  out. 
If  the  ammonia  water  from  gas  factories  be  used  instead 


ALUMINUM  AND  ITS  COMPOUNDS  267 

of  the  potash  salts,  ammonia  alum  is  obtained,  represented 
by  the  formula  (NH4)2A12(SO4)424H2O.  This  is  used 
very  largely  instead  of  the  potash  alum. 

13.  The  term   alum   is  also  applied  to  many  double 
sulphates  which  contain  no  aluminum,  as,  for  example, 
K2Cr2(SO4)4,  potassio-chromic  alum.     In  such  cases  the 
compound  is  designated  by  the  names  of  both  of  the  metals 
entering  into  the  compound.     By  studying  the  formulae 
for  the  alums  mentioned  above,  it  will  be  seen  that  the 
first  metal  is  always  univalent  and  the  second  usually  triv- 
alent.      If,  then,  we  represent  the  univalent  metals  by 
M  and  the  trivalent  by  R,  we  may  write  as  the  general 
formula  for  the  alums,  M2R2(SO4)4,  in  which  Mis  usually 
potassium,  sodium,  or  ammonium,  and  R  aluminum,  iron, 
or  chromium. 

EXERCISE.  —  Write  formulae  for  sodium  alum,  ammonio-ferric  alum, 
potassium  alum,  sodio-chromic  alum,  potassio-ferric  alum,  and  ammonio- 
chromic  alum. 

14.  Alum  possesses  a  sweetish,  astringent  taste,  and 
upon  heating  readily  gives  up  its  water  of  crystallization. 
In  doing  so  it  crumbles  to  an  opaque  mass,  and  in  this 
form  is  known  as  burnt  alum. 

15.  Uses.  — In  medicine,  alum  is  used  as  an  astringent. 
It  checks  bleeding  by  contracting  the  tissues,  and  in  the 
form  of  burnt  alum  it  serves  as  a  mild  caustic  agent, 
especially  for  ulcerations  of  the  mouth.     In  the  arts  alum 
is  used  largely  as  a  mordant,  that  is,  to  fix  the  color  in 
dyeing  cloth. 

EXPERIMENT  157. — In  a  solution  of  logwood  heat  two  pieces  of 
cloth  for  several  minutes,  or  until  both  are  well  colored.  Now,  re- 
move and  allow  them  to  dry.  Then  immerse  one  in  a  strong  solution 
of  alum  and  let  it  stand  a  few  minutes;  remove,  and  when  dry  wash 
both  in  water.  Which  retains  its  color  the  better? 


268  MODERN  CHEMISTRY 

16.  Alum  is  also  used  frequently  as  a  component  of 
baking  powders,  sometimes  in  very  considerable  quantities. 

EXPERIMENT  158.  —  Examine  a  number  of  specimens  of  baking 
powder  for  alum  and  state  results.  Test  them  as  follows:  Put  about 
a  half  gram  of  baking  powder  into  a  test-tube  with  4  or  5  cc.  of  water 
and  a  little  hydrochloric  acid.  Heat  gently  for  a  few  moments,  or 
until  the  solution  is  clear.  If  necessary,  filter  so  as  to  obtain  a  per- 
fectly clear  solution ;  then  add  a  few  drops  of  ammonia,  or  enough  to 
make  it  alkaline.  If  alum  is  present,  a  more  or  less  heavy  precipitate, 
•white  or  nearly  transparent,  will  form.  Some  idea  of  the  amount  of 
alum  present  may  be  obtained  by  the  quantity  of  the  precipitate 
formed.  This,  however,  should  be  verified  by  further  tests. 

17.  ;  Clarifying  Water.  —  In  large  cities  obtaining  their 
water  supply  from  rivers  which  are  muddy  during  cer- 
tain seasons  of  the  year,  considerable  quantities  of  alum 
are  used  for  settling  the  sediment.     Weighed  amounts  of 
lime  and  alum  are  thrown  into  the  settling  basins  ;  the 
lime,  on  coming  into  contact  with  the  water,  is  slaked,  as 
you  have  learned,  forming  calcium  hydroxide,  thus  :  — 

CaO  +  H2O  =  Ca(OH)2. 

This  is  a  strong  alkali,  like  ammonia,  and  forms  in  the 
water  with  the  alum  a  precipitate  of  aluminum  hydroxide, 
A12(OH)6,  just  as  the  ammonia  did  with  the  alum  in  the 
baking  powders.  The  reaction  is  as  follows  :  — 

A12(S04)3  +  3  Ca(OH)2  =  A12(OH)6  +  3  CaSO4. 

Aluminum  hydroxide  is  a  gelatinous  or  starchy  precipi- 
tate which  in  settling  brings  down  with  it  practically  all 
of  the  sediment,  leaving  the  water  clear.  The  only  sub- 
stance added  to  the  water  is  calcium  sulphate,  which,  as 
seen  in  the  study  of  calcium,  simply  renders  the  water  a 
little  more  "hard."  No  trace  of  alum  will  be  found  to 
remain  in  the  water,  since  the  hydroxide  is  insoluble. 


ALUMINUM  AND  ITS  COMPOUNDS  269 

18.  Aluminum  Hydroxide,  A12(OH)6.  —  This,  as  stated 
above,  is  a  starchy,  white,  semi-translucent  precipitate, 
formed  when  ammonia  is  added  to  any  aluminum  salt  in 
solution.  It  may  also  be  formed  by  adding  caustic  soda 
to  a  solution  of  an  aluminum  salt,  but  in  excess  of  this 
reagent  it  is  soluble. 

EXPERIMENT  159.  —  Prepare  some  aluminum  hydroxide  as  de- 
scribed above,  using  ammonia.  Notice  its  appearance,  and  test  its 
solubility  in  hydrochloric  acid.  What  results?  Write  the  reactions. 

Repeat  the  experiment,  using  caustic  soda  or  potash  instead  of  the 
ammonia.  Add  cautiously  a  drop  at  a  time  until  the  precipitate 
forms,  and  then  an  excess.  State  results.  Write  the  two  reactions, 
knowing  that  in  the  latter  case  potassium  aluminate,  K3A1O3,  a  com- 
pound soluble  in  water,  is  formed. 

REVIEW  OF   WORK  IN  ALUMINUM 

Abundance  of  the  metal. 

Form  in  which  it  occurs. 
Former  methods  of  obtaining  it  and  cost. 
Present  methods  of  reduction. 
Description  of  the  metal. 

Color,  density,  melting  point,  malleability,  tenacity,  conductivity, 

ease  of  oxidation,  susceptibility  of  polish. 
Value  of  the  metal  in  a  practical  way. 
Minor  uses  —  Alloys. 
As  a  substitute  for  (sdj&per ;  for  iron. 
Compounds  —  Native. 

Difference  between  kaolin  and  clay. 

Uses  of  the  former. 

Difference  between  emery  and  certain  gems. 

Artificial  compounds. 
Alums  —  Meaning  of  the  term. 
Preparation  of  common  alum. 
What  is  burnt  alum. 
Uses  of  common  alum. 

Chemistry  of  its  use  in  clarifying  water. 

Method  of  showing  its  presence  in  baking  powders. 

Mordant  —  Meaning  of  term. 


CHAPTER   XXIII 
TIN  AND  LEAD 
TIN:  Sn  =  118 

1.  Source  of  Supply.  —  Almost  the  entire  commercial 
supply  of  tin  is  obtained  from  the  ore,  cassiterite,  SnO2, 
sometimes  called  tin-stone.     The  ore  probably  received  its 
technical  name  from  an  early  appellation  of  the  British 
Isles,  Cassiterides.     Extensive  mines  located  at  Cornwall, 
England,  have  been  worked  for  hundreds  of  years.     Long 
before  the   Christian  era  the    Phoenicians  brought  back 
great  quantities  of   ore  from  these  mines ;    yet  even  to 
this  day  they  are  very  productive.     They  extend  down 
into  the  earth  thousands  of  feet,  and  far  out,  even  under 
the  bed  of  the  ocean.     The  purest  tin  is  said  to  be  that 
obtained  from  India,  known  as  Banca  tin.     Other  sources 
of  supply  are  Australia,  Bolivia,  and  the  Black  Hills  of 
Dakota ;    the  last-named   mines,  however,  have  not  yet 
been  well  developed. 

2.  Reduction  of  Ore.  —  With  cassiterite  there  are  usually 
found  small  quantities  of  arsenic  in  the  form  of  arsenic 
sulphide,  besides  some  other  metals.     After  crushing  the 
ore,  it  is  strongly  heated  in  a  reverberatory  furnace,  where 
the  volatile  products,  such  as  arsenic  and  sulphur,  are 
expelled.     At  the  same  time  the  sulphides  of  the  other 
metals  are  converted  into  sulphates,  thus :  — 

CuS  +  2  O2  =  CuSO4. 

270 


TIN  AND  LEAD  271 

These  sulphates  are  soluble  in  water,  and  to  remove  them 
the  roasted  ore  is  thoroughly  washed;  it  is  then  mixed 
with  coke  or  coal  and  reduced  in  a  blast  furnace,  the 
carbon,  as  usual,  serving  to  deoxidize  the  cassiterite.  This 
last  process  may  be  indicated  thus :  — 

Sn02  +  2  C  =  Sn  +  2  CO. 

EXPERIMENT  160.  —  If  granulated  tin  is  not  to  be  had,  some  foil, 
procured  from  the  tobacconist,  will  serve.  Test  the  melting  point  of 
tin  by  holding  a  small  piece  in  the  flame.  Try  the  effect  of  nitric  acid 
upon  tin.  Also  hydrochloric,  and  state  results.  Try  it  on  charcoal 
with  the  oxidizing  flame.  State  results.  Does  tin  oxidize  readily  at 
ordinary  temperatures? 

Heat  a  piece  of  "  tin  plate  "  in  the  burner  flame  a  moment,  and  then 
plunge  it  into  cold  water.  Now  rub  the  surface  with  a  cloth  mois- 
tened with  diluted  aqua  regia,  and  wash  with  water.  State  the  appear- 
ance of  the  surface. 

3.  Characteristics  of  Tin.  —  Tin  is  a  silvery  white,  lus- 
trous metal  which  does  not  tarnish  in  the  air.  It  is  some- 
what harder  than  lead,  but  melts  at  a  lower  temperature. 
By  the  oxidizing  flame  it  may  be  converted  into  a  white 
powder,  SnO2.  It  is  highly  crystalline  in  structure,  as 
may  be  seen  by  removing  the  surface  of  a  sheet  or  bar  of 
tin  with  acid.  The  crystals  may  be  prepared  by  melting 
some  tin  in  a  crucible,  and  when  it  is  partially  cooled, 
pouring  out  what  is  still  molten.  When  a  bar  of  tin  is 
bent,  these  crystals  rub  together,  and  produce  a  distinctly 
audible  sound,  known  as  the  "tin  cry."  This  metal  is 
very  malleable,  and  may  easily  be  beaten  or  rolled  into 
thin  sheets.  It  is  soluble  in  aqua  regia  and  in  hydro- 
chloric acid,  but  ordinary  nitric  acid  converts  it  into  a 
white  powder,  metastar.nic  acid,  from  which  we  may 
obtain  stannic  oxide,  SnO2,  by. expelling  the  water. 


272  MODERN  CHEMISTRY 

4.  Uses.  —  Because  of  its  permanency  in  the  air,  tin  is 
used  in  coating  sheet  iron,  making  what  is  known  as  tin 
plate.     From  this  all  "tin  "  vessels  are  made.     In  making 
sheet  tin,  the  sheet  iron  is  first  thoroughly  cleansed  by 
immersion  in  dilute  acids,  then  washed  and  dried.     It  is 
next  dipped  into  a  bath  of  molten  tin,  of  which  a  thin 
coating  adheres  to  the  iron.     A  second  and  a  third  dipping 
increase  the  thickness  of  the  coating.     For  outdoor  work, 
such  as  roofing  and  guttering,  a  heavier  quality  of  sheet 
iron  is  used,  and  the  tin  is  generally  alloyed  with  lead 
because  the  latter  is  much  cheaper. 

5.  In  the  form  of  foil,  tin  is  extensively  used  for  wrap- 
ping purposes ;  at  present,  however,  it  is  often  adulter- 
ated with  lead,  especially  in  cases  where  the  latter  metal 
will  be  of  no  disadvantage.     Tin  foil  amalgamated  with 
mercury  is  also  used  frequently  for  the  backs  of  mirrors. 

6.  As  stated  elsewhere,  tin  is  used  extensively  in  alloys, 
among    them    being    common     solder,    type    metal,    bell 
metal,  and   the  fusible  metals.     To    these  it  imparts  the 
property  of  a  low  melting  point,  that  of  the  fusible  metals 
being  even  lower  than  the  boiling  temperature  of  water. 
Spoons  made  from  these  metals,  if  dipped  into  a  cup  of 
hot  tea  or  coffee,  would  rapidly  melt  and  disappear. 

Compounds  of  Tin 

7.  Stannous  and  Stannic  Salts.  —  As  is  the  case  with 
many  other  metals,  tin  forms  two  general  classes  of  salts : 
the  stannous  and  the  stannic. 

8.  The  Chlorides :  Stannous,  SnCl2,  and  Stannic,  SnCl4.  — 
The  former  is  a  white  crystalline  salt  which  may  be  pre- 
pared by  dissolving  tin  in  hydrochloric  acid.    It  is  a  great 
reducing  agent,  and  readily  reduces  mercury  from  certain 
of  its  salts.     If  a  solution  of  stannous  chloride  be  erradu- 


TIN  AND  LEAD  273 

ally  added  to  one  of  mercuric  chloride,  at  first  a  white 
precipitate  of  mercurous  chloride  forms,  and  then  by  the 
addition  of  more  of  the  tin  solution,  the  precipitate  slowly 
turns  darker  from  the  fact  that  the  mercury  is  reduced  to 
the  metallic  condition,  though  in  a  very  finely  divided 
form.  The  following  reactions  express  the  changes  that 
take  place :  — 

2  HgCl2  +  SnCl2  =  Hg2Cl2  +  SnCl4; 
Hg2Cl2  +  SnCl2  =  Hg2       +SnCl4. 

Various  other  metallic  salts  are  in  a  similar  way  reduced 
from  the  ic  to  the  ous  condition.  The  above  reaction  of 
stannous  chloride  and  mercuric  chloride  upon  each  other 
may  be  used  as  a  test  for  the  presence  of  either  metal. 

9.    Stannic  chloride  may  be  prepared  by  dissolving  tin 
in  aqua  regia. 

EXPERIMENT  161.  —  Dissolve  some  tin  in  hydrochloric  acid,  and 
boil  nearly  to  dryness  to  expel  the  excess  of  acid.  Take  up  with  a 
few  cubic  centimeters  of  water,  and  gradually  add  it  to  a  little  of 
a  solution  of  mercuric  chloride  in  a  test-tube.  Do  you  obtain  first  a 
white  precipitate,  and  afterward  a  gray  one,  becoming  nearly  black, 
as  explained  in  the  text  above  ?  If  necessary,  warm  gently. 

Dissolve  a  little  tin  in  hydrochloric  acid  with  a  little  nitric  added; 
boil  nearly  dry,  and  after  adding  a  few  cubic  centimeters  of  water, 
test  with  mercuric  chloride,  as  before.  State  the  results. 

10.  The  Sulphides :  Stannous,  SnS,  and  Stannic,  SnS2-  - 
These  may  be  prepared  by  passing  a  current  of  hydrogen 
sulphide  through  solutions  of  stannous  and  stannic  chloride, 
respectively.  The  former  is  a  dark  brown  precipitate, 
the  latter,  bright  yellow,  closely  resembling  arsenic  sul- 
phide. These  two,  though  alike  in  some  respects,  differ, 
however,  in  that  the  latter  is  soluble  in  ammonium  car- 
bonate, while  the  former  is  not.  Stannic  sulphide,  more- 


274  MODERN  CHEMISTRY 

rover,  is  soluble  in  hot  concentrated  hydrochloric  acid, 

while  the  arsenic  is  not. 

V 

EXPERIMENT  162.  —  Add  a  drop  or  two  of  hydrochloric  acid  to  a 
X  solution  of  stannous  ckloride,  and  pass  through  it  a  current  of  hydro- 
gen sulphide.  Describe  the  precipitate  which  forms.  Write  the 
reaction.  Treat  a  solution  of  stannic  chloride  in  the  same  way;  what 
are  the  results  ?  Write  the  reaction.  Take  a  part  of  this  precipitate 
and  add  a  little  yellow  ammonium  sulphide  ;  what  happens  ?  To  the 
"\remainder  add  some  ammonium  carbonate  solution.  Is  the  sulphide 
dissolved?  ^  . 

11.  Stannic  Oxide,  Sn02.  —  This  is  principally  of  in- 
terest because  it  is  the  chief  ore  of  tin.     It  is  obtained 
when  tin  is  strongly  heated  with  the  oxidizing  flame ;  it 
is  pale  yellow  when  hot,  but  white  when  cold. 

EXERCISE.  —  Write  the  reactions  showing  the  preparation  of  all  the 
above-named  compounds. 

EXPERIMENT  163.  —  To  determine  whether  any  specimen  of  tin 
contains  lead  as  an  adulterant.  Poisoning  sometimes  results  from  the 
canning  of  fruit  in  tin  which  is  alloyed  with  lead.  Procure  any 
specimens  of  tin  plate,  or  foil,  and  put  upon  them  a  drop  or  two  of 
nitric  acid.  When  dry,  add  a  little  of  a  solution  of  potassium  iodide 
to  the  same  spots.  If  the  tin  is  adulterated  with  lead,  bright  yellow 
spots  will  appear,  owing  to  the  formation  of  lead  iodide. 

LEAD:  Pb  =  207 

12.  History.  —  Lead  has  been  known  from  very  early 
times  because  of  the  ease  with  which  it  is  reduced  from 
its   ores.       It    is    mentioned    several    times    by  -  biblical 
writers,  but  seems  to  have  been   confounded  with  tin. 
The  two  metals  are  spoken  of  by  Latin  writers  as  black 
and  white  lead,  respectively ;  yet  tin  was  the  more  expen- 
sive, and  known  to  be  suitable  for  soldering. 

13.  Occurrence.  —  The  principal  ore  of  lead  is  galena, 
or  lead  sulphide,  PbS.     It  is  a  dark-colored,  almost  black, 


TIN  AND  LEAD 


275 


lustrous  mineral,  resembling  somewhat  metallic  lead  itself, 
but  does  not  tarnish  in  the  air  as  the  metal  does.  It 
occurs  in  masses  which  tend  to  split  up  into  cubical  form  ; 
it  is  widely  distributed,  but  is  usually  found  in  what  are 
called  "  pockets."  It  has  very  frequently  associated  with 
it  ores  of  zinc,  silver,  iron,  and  some  other  metals. 

EXPERIMENT  164.  —  Put  into  a  small  cavity  in  a  stick  of  charcoal 
a  little  lead  oxide,  PbO,  or  minium,  Pb3O4,  or  powdered  galena,  and 
heat  with  the  reducing  flame  before  the  blowpipe.  Do  you  obtain  a 
metallic  globule? 

14.  Reduction  of  the  Ores.  —  This  experiment  illustrates 
in  the  main  what  is  usually  known  as  the   "carbon   re- 
duction."    The  furnace  used  in  this  method  is  not  essen- 
tially different  from  the  blast  furnace  shown  under  iron, 
for  the  reduction  of  iron  ores.     See  the  illustration  on 
page  301. 

15.  The  Oxidation  Process.  —  The  second  method  may 
be  called  the  "roasting"  or  "oxidation"  process.     The 
finely  ground  ore  is  placed  upon  the  floor  of  the  oven  in  a 
reverberatory    furnace    (see 

Fig.  57).  The  heat  and 
flames  are  directed  down- 
ward from  the  arching  roof 
above  upon  the  ore.  In  this 
way  the  upper  layers  are 
converted  from  the  sulphide 
into  the  oxide,  as  seen  in  the 
reaction :  — 


FIG.  57. 


PbS  +  3  O  =  PbO  +  SO3. 

The  central  portion  of  the  mass  being  less  strongly  heated 
is  converted  into  the  sulphate,  thus  :  — 

PbS  +  2  O2 


276  MODERN  CHEMISTEY 

The  bottom  portions  of  ore,  not  receiving  sufficient  heat, 
undergo  110  chemical  change.  When  sufficient  time  has 
elapsed  to  secure  the  above  results,  the  strong  draughts 
of  air  are  shut  off,  in  order  to  prevent  the  process  of 
oxidation  from  going  further;  thereupon  the  unchanged 
sulphide,  PbS,  reacts  upon  the  oxide,  PbO,  and  the  sul- 
phate, PbSO4,  already  formed,  whereupon  metallic  lead  is 
obtained.  We  may  represent  this  by  the  following  reac- 
tions :  — 

PbS  +  2  PbO  =  3  Pb  +  S02, 

and  PbS  +  PbSO4  =  2  Pb  +  2  SO2, 

or  representing  the  complete  change  by  a  single  reaction, 
2  PbS  +  2  PbO  +  PbSO4  =  5  Pb  +  3  SO2. 

This  is  the  process,  probably,  most  commonly  used,  because 
the  most  economical,  but  it  is  adapted  only  to  moderately 
rich  ores. 

16.  Reduction  of  Impure  Ores. — When  the  lead  ores 
are  considerably  mixed  with  the  ores  of  other  metals,  the 
processes  described  above  are  not  satisfactory. 

EXPERIMENT  165.  —  Suspend  in  a  test-tube  or  bottle,  about  two- 
thirds  full  of  a  moderately  strong  solution  of  lead  acetate,  a  strip  of 
zinc.  Allow  it  to  stand  for  several  hours  without  shaking.  Notice 
the  flaky  crystals  of  lead  that  form  on  the  zinc,  giving  what  is  called 
the  "  lead  tree."  After  24  to  48  hours  carefully  lift  out  the  « tree," 
remove  the  crystals  of  lead,  and  notice  how  soft  and  porous  the  mass 
seems.  Notice  how  the  zinc  strip  has  changed.  If  you  test  the  solu- 
tion in  the  bottle,  you  will  find  that  it  contains  zinc  now  instead  of 
lead.  That  is,  as  the  lead  has  slowly  deposited  upon  the  zinc,  the 
zinc  has  likewise  slowly  dissolved.  The  chemical  change  is  shown  by 
the  following  reaction :  — 

Pb(C2H302)2  +  Zn  =  Zn(C2H302)2  -f  Pb. 


TIN  AND  LEAD  277 

17.  For  impure  ores  a  similar  method  is  adopted.     They 
are  mixed  with  scrap  iron,  and  melted  in  a  furnace,  where- 
upon the  lead,  together  with  any  silver  present,  is  set  free, 
and  the  iron  combines  with  the  other  matters  present. 

Thus  :  — 

PbS  +  Fe  =  FeS  +  Pb. 

18.  Characteristics  of  Lead.  —  Many  of  these  may  be 
learned  from  the  following  simple  experiments:  — 

EXPERIMENT  166.  —  Take  the  globule  of  lead  obtained  in  Experi- 
ment 164,  and  cut  it  with  your  knife.  What  can  you  say  of  its  hard- 
ness ?  its  color ?  its  luster?  Does  it  retain  this  luster?  Test  its  melting 
point  with  the  blowpipe  and  state  results.  What  proof  can  you  give 
that  it  oxidizes  in  the  air?  Try  it  on  charcoal  with  the  oxidizing 
flame;  what  is  seen  upon  the  charcoal  around  the  metal?  Compare 
it  with  silver  in  this  respect.  Put  a  small  piece  of  lead  into  a  test-tube 
and  determine  whether  it  is  soluble  in  nitric  acid;  in  hydrochloric 
acid. 

19.  Lead  is  a  very  heavy,  soft,  malleable,  dark  gray 
metal,  with  a  specific  gravity  of  11.3  and  a  melting  point 
of  about  330°.     It  has  a  brilliant  luster  when  first  cut ; 
but,  owing  to  the  fact  that  it  so  readily  oxidizes  in  the 
air,  the  surface  is  soon  tarnished.     This  coating,  however, 
protects  the  metal  from  further  oxidation,  and  it  is  very 
durable.     Lead  is  very  different  from  iron  in  this  respect, 
as  the  layer  of  rust,  oxide,  that  forms  upon  the  latter  metal 
on  exposure  does  not  protect  it.     Lead  is  slightly  soluble 
in  ordinary  water,  and  as  all  lead  salts  are  very  poisonous, 
water  that  has  stood  in  leaden  pipes  any  considerable 
length  of  time  should  not  be  used.     The  effects  of  lead 
compounds  upon  the  human  system  are  often  seen  among 
painters,  who  suffer  from  what  is  known  as  "lead  colic." 

20.  Uses  for  Lead.  —  This  metal,  as  well  as  its  com- 
pounds, has  almost  numberless  uses.    One  of  the  most  im- 


278  MODERN  CHEMISTRY 

portant  is  for  lead  pipes  in  plumbing,  used  because  they 
may  be  bent  with  ease.  It  is  also  employed  largely  for 
underground  telephone  conduits  in  cities,  as  well  as  for 
casings  or  sheaths  for  bundles  of  overhead  wires.  This 
pipe  is  made  by  forcing  lead  at  a  temperature  near  the 
point  of  solidification  through  an  annular  opening  in  a 
steel  plate. 

21.  Shot.  —  Another  use  of  lead  is  in  making  shot  and 
bullets.     As  stated  elsewhere,  for  this  purpose  arsenic  in 
small  quantities  is  alloyed  with  the  lead.     One  method  is 
to  allow  the  molten  alloy  to  flow  into  a  perforated  vessel, 
from  which  the  streams  of  metal  fall  long  distances  into 
water.     In  the  descent  the  streams  are  broken  into  glob- 
ules, which   before    reaching   the  water  have  solidified. 
The  various  sizes  and  shapes  thus  obtained  must  next  be 
sorted.     The  shot  are  allowed  to  roll  down  over  inclined 
screens  with  a  mesh  of  different  sizes.     The  smaller  shot 
will  drop  through  first  into  one  bin,  the  next  size  into  a 
second,  and  so  on.     The  irregular-shaped  pieces  will  not 
roll  through,  and  eventually  make  their  way  off  the  end 
of  the  plane.     The  shot  are  next  polished  by  rotating  in 
cylinders  containing  a  little  powdered  graphite. 

22.  Type   Metal. — A  third   important   use   is   in   the 
manufacture  of  type  for  printers.    This  is  made  of  an  alloy 
of  lead,  tin,  and  antimony,  or  bismuth.     The  latter  metals 
are  used  to  give  hardness  to  the  alloy  and  to  secure  ex- 
pansibility at  the  moment  of  cooling.      Owing  to   this 
property  the  type  has  clear,  sharply  cut  faces,  whereas 
lead  alone  would  produce  that  having  a  battered  or  worn- 
out  appearance. 

23.  Solder.  — A  fourth  use  of  lead  is  in  solder,  an  alloy 
of  tin  and  lead,  the  ordinary  proportions  being  half  and 
half.     The  tin  is  added  to  secure  a  low  melting  point,  and 


TIN  AND  LEAD  279 

the  proportions  vary  according  to  the  use  to  which  the 
solder  is  to  be  put.  Lead  is  also  used  in  making  pewter, 
an  alloy  of  lead  and  tin,  and  in  storage  batteries,  but 
never  for  "lead"  pencils. 

Compounds  of  Lead 

There  are  many  of  these,  the  most  important  among 
them  being  the  following  :  — 

24.  Lead  Acetate,  Pb(C2H302)2,  known  also  as  Sugar  of 
Lead,  because  of  its  sweet  taste.     It  is  a  white  crystalline 
salt,  which  may  be  obtained  by  dissolving  lead  in  vinegar 
or  acetic  acid,  HC2H3O2.     It  is  used  frequently  for  dye- 
ing, and  in  medicine  as  an  external  application  for  ivy 
poisoning  and  in  acute  cases  of  erysipelas. 

25.  Lead  Chloride,  PbCl2. — This  may  be  prepared  by 
adding  hydrochloric  acid  to  a  lead  solution,  especially  the 
acetate.    It  is  a  white  solid,  somewhat  soluble  in  cold  water, 
completely  so  in  hot  water,  from  which  it  crystallizes  out 
upon  cooling  in  small  crystals  that  rapidly  settle. 

EXPERIMENT  167.  —  To  a  few  cubic  centimeters  of  a  solution  of 
lead  acetate,  or  nitrate,  in  a  test-tube,  add  about  1  cc.  of  hydrochloric 
acid.  Note  the  results.  Write  the  reaction.  Now  add  a  little  water 
and  heat  the  contents  of  the  tube  to  the  boiling  point.  What  hap- 
pens ?  Allow  it  to  cool  and  watch  the  tube  meanwhile ;  what  happens? 
How  do  the  two  solids  differ  in  appearance? 

26.  Lead  Sulphate,  PbS04.  —  This  may  be  prepared  by 
adding  sulphuric  acid  to  a  soluble  lead  salt,  as  the  acetate 
or  nitrate.     It  is  a  heavy  white  salt,  very  slightly  soluble 
in  water  and  almost  entirely  insoluble  in  alcohol. 

27.  Lead  Nitrate,  Pb(N03)2.  —  This  salt  is  obtained  when 
lead  is  dissolved  in  nitric  acid.     It  is  a  white,  crystalline 
compound,  soluble  in  water.     It  is  used  somewhat  in  the 
laboratory. 


280  MODERN  CHEMISTRY 

28.  The  Oxides.  —  There  are  several  oxides  of  lead,  the 
most  important  of  which  are  PbO,  litharge,  or  lead  oxide  ; 
PbO2,  lead  peroxide ;   and  Pb3O4,  minium,  or  red  lead. 
This  last  is  a  deep  red  compound,  used  in  plumbing  to 
secure  tight  joints,  and  is  sometimes  regarded  as  a  salt 
of  plumbic  acid,  thus  :  — 

Pb2PbO4  from  H4PbO4. 

It  may  be  prepared  from  lead  oxide,  PbO,  by  heating. 
Litharge  is  a  light  brown-colored  powder,  obtained  in 
large  quantities  when  argentiferous  lead  ores  are  reduced 
by  the  cupellation  process,  and  is  always  produced  when 
lead  is  heated  strongly  in  the  air.  It  is  used  frequently 
in  storage  batteries,  in  preparing  red  lead,  as  stated  above, 
and  in  making  flint  glass,  to  which  it  seems  to  impart  the 
qualities  of  high  refraction,  almost  perfect  transparency, 
and  softness. 

29.  Lead  Carbonate,  PbC03.  — This  is  an  insoluble  white 
compound,  which  may  be  obtained  by  treating  a  solution 
of   lead   nitrate  with  one  of  ammonium  carbonate.      If 
sodium  carbonate  is  used  instead  of   the  ammonium,  a 
basic  carbonate  is  obtained,  or  what  may  be  represented 
by  the  formula,  2  PbCO3,  Pb(OH)2,  that  is,  two  molecules 
of  lead  carbonate  combined  with  one  of  lead  hydroxide. 
In  commerce  this  is  known  as  white  lead,  and  is  used  very 
extensively  as  paint. 

30.  White  lead  is  prepared  by  several  methods,  the 

oldest  and  perhaps  the  best  being  that  known 
as  the  "Dutch  method"  (see  Fig.  58). 
Glazed  earthen  jars,  8  or  9  inches  in  height, 
are  used.  About  3  inches  from  the  bottom 
on  the  inside  are  some  projections,  upon 
FIG.  58.  which  a  small  board  rests.  Beneath  the 


TIN  AND  LEAD  281 

shelf  is  vinegar,  v,  and  above  it  a  coil  of  sheet  lead,  a. 
Hundreds  of  these  jars  so  prepared  are  placed  side  by 
side  and  covered  with  tan  bark  ;  above  them  another 
layer  of  jars  with  a  covering  of  bark  is  placed,  and  so  on, 
to  a  considerable  height.  The  whole  is  then  buried  under 
compost,  which  in  decaying  generates  not  a  little  heat. 
The  fumes  of  acetic  acid  act  upon  the  lead,  gradually 
converting  it  into  lead  acetate.  Then  the  carbon  dioxide 
set  free  from  the  decaying  tan  bark  combines  with  the 
acetate,  slowly  changing  it  into  the  basic  carbonate.  Sev- 
eral weeks  are  required  for  the  completion  of  the  process. 
The  white  lead  is  next  removed  from  the  jars,  washed  to 
dissolve  out  any  lead  acetate  remaining,  then  ground  in 
oil,  and  is  ready  for  use 

31.  Milner's  Method. — Numerous  attempts  have  been 
made  to  devise  a  method  whereby  white  lead  could  be 
made  quickly.      One  of   these,  which  is  fairly  good,  is 
Milners.     Four  parts  of  litharge,  PbO,  are  mixed  with 
one  of  common  salt,  NaCl,  and  sixteen  of  water.     The 
whole  is  ground  together  in  a  mill   for  4  or  5  hours, 
then  transferred   to  a  leaden  vessel,  into  which  is  con- 
ducted a  current  of  carbon  dioxide  until  the  whole  is 
neutral. 

32.  White  Lead  by  Electrolysis.  —  A  current   of  elec- 
tricity is  passed  through  a  solution  of  sodium  nitrate  in 
water,   in  which  a  bar  of   lead  is  suspended.      By  the 
electric  current  the  sodium  nitrate  is  decomposed,  forming 
caustic  soda  and  nitric  acid,  thus  :  — 

NaN03  +  H20  =  HN03  +  NaOH. 

The  nitric  acid  thus  produced  attacks  the  lead,  and 
converts  it  into  lead  nitrate,  Pb(NO3)2.  A  second 
reaction  follows,  the  lead  nitrate  and  caustic  soda 


282  MODERN  CHEMISTRY 

combining  to  form  lead  hydroxide  and  sodium  nitrate, 
thus : — 

Pb(NO3)2  +  2  NaOH  =  Pb(OH)2  +  2  NaNO8. 

Thus  we  have  produced  again  the  same  solution  we  had 
in  the  beginning,  and  only  the  lead  needs  to  be  renewed. 
The  lead  hydroxide  thus  obtained  is  treated  next  with  so- 
dium carbonate,  when  basic  lead  carbonate  is  obtained,  as 
follows :  — 

2  Pb(OH)2  +  Na-2CO8  =  2  NaOH  +  PbCO3,  Pb(OH)2. 

This  process  is  continuous,  very  rapid,  and  is  said  to 
produce  a  fairly  good  quality  of  white  lead. 

33.  Lead  Chromate,  PbCr04.  —  This  is  an  insoluble  com- 
pound of  bright  yellow  color,  and  is  easily  prepared  by  add- 
ing a  solution  of  potassium  dichromate  to  one  of  a  lead 
salt.     It  is  used  to  a  considerable  extent  as  a  paint,  being 
sold  under  the  name  chrome  yellow. 

EXPERIMENT  168.  —  Let  the  student  prepare  some  of  this  pigment, 
and  examine  it.  Use  either  potassium  chromate  or  dichromate  with 
a  solution  of  lead  nitrate  or  acetate. 

34.  Lead  Sulphide,  PbS. — This  is  an  insoluble  com- 
pound, black  in  color,  prepared  by  passing  a  current  of 
hydrogen  sulphide  through  a  solution  of  lead  nitrate  or 
acetate.     It  has  the  same  composition  as  native  galena, 
but  lacks  the  metallic  luster.     Galena  is  used  in  glazing 
pottery  ware,  except  such  as  is  to  be  used  for  articles  of 
food.     It  is  ground  fine,  mixed  with  pulverized  clay  and 
water,  and  the  mixture  washed  over  the  pottery.     When 
the  vessels  are  strongly  heated  in  ovens,  the  silica  in  the 
clay  and  the  lead  sulphide  melt  and  form  a  glass  which 
fills  the  pores  of  the  clay.    As  such  glazes  are  soluble,  they 
are  not  suitable  for  pottery  of  all  kinds. 


TIN  AND  LEAD  283 

EXERCISE.  —  Write  the  reactions  expressing  the  preparation  of  all 
the  lead  salts  described  above. 

35.  Identification.  —  Any  solution  of  a  lead  salt  may  be 
identified  by  adding  to  it  sulphuric  acid  or  potassium 
dickromate,  as  in  preparing  the  sulphate,  or  chromate, 
described  above.  A  solution  of  potassium  iodide  is  some- 
times used  with  the  lead  solution,  and  gives  a  bright 
yellow  precipitate  resembling  chrome  yellow. 

EXPERIMENT  169.  —  To  determine  the  composition  of  common 
solder.  Add  to  a  small  piece,  not  larger  than  a  grain  of  wheat, 
about  a  cubic  centimeter  of  concentrated  nitric  acid,  and  warm 
gently.  When  the  alloy  has  disappeared,  and  the  white  powder 
which  has  formed  is  settled,  decant  the  clear  solution  into  an  evapo- 
rating dish.  Add  some  water  to  the  white  powder,  and  decant  again. 
Now  evaporate  the  solution  decanted  nearly  to  dryness,  add  a  little 
water,  and  make  two  tests  for  lead  with  separate  portions  of  it, 
according  to  method  of  identification  suggested  above.  State  your 
conclusion. 

To  the  white  powder  obtained  at  the  beginning,  add  a  little  strong 
hydrochloric  acid,  and  heat  until  solution  is  secured.  Boil  down 
nearly  to  dryness,  add  25  to  50  cc.  of  water,  and  through  part  of  it 
pass  hydrogen  sulphide ;  to  another  portion  add  slowly,  drop  by  drop, 
mercuric  chloride.  State  results.  From  these  can  you  determine 
what  metal  you  have  ?  See  section  9,  page  273,  and  compare  results. 

SUMMARY  OF  CHAPTER 

History  of  tin  and  lead. 

Occurrence  of  each  —  Chief  ore,  and  its  composition. 

Principal  tin  mines  —  Description. 
Reduction  of  the  ores. 

Wherein  similar. 

Purpose  of  the  roasting  in  each  case. 

Description  of  a  second  method  of  reducing  lead. 
Furnace  used. 
Chemical  changes  and  reactions. 

Experiment  of  "lead  tree"  —  Description  —  Purpose. 


284  MODERN  CHEMISTRY 

Characteristics  of  lead  and  tin  —  Compare  them  in 
Color. 
Density. 
Hardness. 
Melting  point. 
Malleability. 
Tendency  to  oxidize. 
Tendency  to  crystallize. 
Solubility  in  acids. 
Uses. 

Sheet  tin  —  What  is  it  ?  —  Its  use  —  How  made  ?  —  Why? 
Alloys  of  tin  —  Properties  secured  by  the  tin. 
Foil  —  Purposes. 

Lead  pipes  —  Use  —  How  made  ? 
Shot  —  Manufacture  of. 
Type  metal. 
Solder. 
Compounds. 

The  oxides  of  tin  and  lead  —  Compare  them. 

Uses  and  preparation. 
Stannous  chloride ;  lead  chloride. 
Preparation  of  each. 
Interesting  facts  about  each. 
The  Sulphides  —  Preparation  of  each. 
Appearance  of  each. 
Uses  of  PbS. 
Other  important  lead  compounds. 

Sugar  of  Lead  —  Chemical  name  and  formula. 
How  prepared. 
Uses. 
White  lead  —  Composition. 

Best  way  of  preparing;  give  plan  and  chemical  reac- 
tions. 

Electrolytjc  method. 
Chrome  yellow. 

How  prepared  in  laboratory. 
Appearance  and  uses. 

Usual  method  of  identification  of  lead  and  tin  salts. 
Analysis  of  common  solder. 


CHAPTER   XXIV 

ARSENIC,  ANTIMONY,  BISMUTH 

ARSENIC  :   As  =  75 

1.  Source  of  Supply.  —  In  limited  quantities  metallic 
arsenic  is  found  free  in  one  or  two  countries  of  Europe, 
especially  Germany.     The  greater  part,  however,  is  ob- 
tained from  arsenical  pyrite,  that  is,  iron  pyrite,  FeS2,  in 
which    arsenic  has  replaced   an   atom   of   sulphur,  thus, 
FeAsS.     It  also  occurs  in  combination  with  other  metals, 
such  as  zinc  and  nickel,  and  with  sulphur,  as  red  arsenic 
sulphide  or  realgar,  As2S2,  and  yellow  arsenic  sulphide, 
As2S3,  or  orpiment. 

2.  Reduction  of  the  Ores.  —  As  already  stated,  arsenical 
pyrite  is  most  commonly  used  for  the  production  of  arsenic. 
This  ore  is  first  roasted  in  ovens  at  a  moderately  strong 
heat,  by  which  it  is  oxidized,  thus  :  — 

2  FeAsS  +  5  O2  =  Fe2O3  -I-  As2O3  +  2  SO2. 

The  last  two  of  these  products  are  volatile  and  are  passed 
over  into  cold  chambers,  where  the  oxide  of  arsenic  con- 
denses as  a  white  sublimate.  This  is  next  mixed  with 
powdered  charcoal,  put  into  retorts,  and  heated.  The 
arsenic  oxide  is  deoxidized  by  the  charcoal,  the  metallic 
arsenic  vaporizes  and  is  condensed  in  cold  chambers, 
thus  :  — 


285 


286  MODERN  CHEMISTRY 

EXPERIMENT  170. — Mix  well  a  little  arsenic  trioxide  and  some 
powdered  charcoal  and  put  into  one  end  of  a  piece  of  hard  glass 
tubing.  Now,  heat  strongly  in  the  Bunsen  flame,  holding  the  tube  in 
a  slanting  position,  with  the  cooler  end  up.  Notice  the  deposit  form- 
ing. Describe  it.  What  has  been  the  effect  of  the  charcoal  ? 

This  experiment  illustrates  the  commercial  method  of  preparing 
arsenic. 

3.  Characteristics  of  Arsenic.  —  In  many  respects  arsenic 
is  not  unlike  some  of  the  non-metallic  elements,  notably 
phosphorus.  ^It   forms   compounds  with   hydrogen  and 
oxygen  similar  to  those  of  phosphorus,  and  with  several 
metals  a  variety  of  salts  in  which  arsenic  is  the  acid- 
forming  element ;  for  example,  sodium  arsenate,  Na3AsO4, 
nickel  arsenide,  NiAs,  etc.     In  general  appearance,  how- 
ever, arsenic  is  more  like  the  metals.      Thu^ttk  is  of  a 

•    '  ** 

dark  gray  color,  with  metallic  luster  when  frfeshly, broken, 
has  a  marked  tendency  to  crystallize,  and  tarnishes  slowly 
in  moist  air.  It  vaporizes  without  molting,  and  when  in 
the  form  of  vapor  has  a  sickening  garlic  odor.  It  is  of 
medium  density,  and,  like  phosphorus,  has  four  atoms  to 
the  molecule.  It  is  but  little  acted  upon  by  nitric  or 
hydrochloric  acid,  but  dissolves  readily  in  aqua  regia  ®r 
nascent  chlorine.  It  has  strong  affinity  for  chlorine,  and 
if  it  43e  finely  powdered  and  sifted  into  a  bottle  of  the  gas 
it  burns  readily. 

EXPERIMENT  171.  — Examine  some  crystals  of  metallic  arsenic  and 
notice  the^r  color  and  general  appearance.  Are  they  malleable?  Heat 
a  small  piece  on  charcoal  withvthe  blowpipe.  Notice  the  odor.  Does 
the  arsenic  melt  ?  What  becomes  of  it  ? 

i^V-'!: 

4.  Uses. — In  the^  metallic  form  arsenic  has  little  use 
except  in  making  shot.     With  lead  it  forms  an  alloy  that 
is  considerably  harder  than  the  former  metal,  and  at  the 
same  time  one  which,  in  the  molten  condition,  is  much 


ARSENIC,  ANTIMONY,  BISMUTH  287 

more  mobile.  This  property  of  the  arsenic  alloy  is  of 
value  in  the  manufacture  of  shot  by  the  ordinary  method, 
for  the  shot  made  from  it  are  more  perfect  in  shape  than 
those  made  from  a  metal  more  viscous,  like  lead. 

Compounds  of  Arsenic 

EXPERIMENT  172.  —  To  study  the  characteristics  of  arsine,  AsH3. 
Prepare  a  flask  for  the  generation  of  hydrogen  from  zinc  and  sulphuric 
acid,  as  on  page  39,  and  attach  a  jet.  After  a  few  moments,  or 
when  sufficient  time  has  elapsed  for  the  air  to  be  expelled,  wrap  a 
towel  around  the  flask  or  inclose  in  a  small  box 
with  an  opening  through  the  cover,  as  seen  in  the 
figure,  and  light  the  jet.  You  have  hydrogen 
burning.  Hold  a  cold  porcelain  dish  against  the 
flame  and  notice  that  no  deposit  forms  upon  the 
dish.. 

Now,  add  to  the  hydrogen  flask  a  little  arsenic 
trioxide,  dissolved  in   dilute   hydrochloric  acid.     I- 
Again  light  the  jet,  and  notice  how  the  color  of 
the  flame  has  changed.     Hold  a  cold  dish  against  FlG> 

the  jet  as  before.  Is  any  deposit  formed?  What 
that  you  have  already  seen  does  it  closely  resemble  ?  The  gas  being 
generated  is  arsine.  Now,  hold  a  beaker  or  test-tube  over  the  burning 
jet,  and  notice  whether  there  are  not  two  different  deposits  formed. 
Can  you  decide  what  they  are?  Write  the  reaction  that  takes  place 
when  arsine  burns. 

5.  Arsine. — Arsine,  AsH3,  is  also  known  as  arseniu- 
reted  hydrogen,  or  hydrogen  arsenide.  It  is  a  compound 
of  considerable  interest,  because  it  is  always  prepared  in 
testing  for  arsenic  in  cases  of  suspected  poisoning.  The 
method  used  is  the  one  described  in  the  experiment 
above.  This  is  known  as  Marsh's  test,  and  is  so  exceed- 
ingly delicate  that  mere  traces  of  arsenic,  even  so  low  as 
one  part  in  several  hundred  thousand,  can  be  detected. 
Care  should  be  taken,  however,  to  see  that  tke  zjjic  is 


288  MODERN  CHEMISTRY 

perfectly  free  from  arsenic.  Antimony  gives  a  spot  con- 
siderably like  that  of  arsenic  seen  above,  but  the  latter 
may  be  detected  by  treating  with  a  solution  of  bleaching 
powder,  in  which  the  arsenic  spots  are  soluble,  while  the 
others  are  not. 

6.  Let  us  study  the  reactions  that  take  place.     First, 
by  the  reaction  of  sulphuric  acid  and  zinc  upon  each  other 
hydrogen  is  produced,  thus  :  — 

Zn  +  H2SO4  =  H2  +  ZnSO4. 

The  hydrogen  atoms  in  the  nascent  condition,  instead  of 
uniting  with  one  another  to  form  molecules  of  hydrogen, 
unite  with  the  arsenic  present,  forming  hydrogen  arsenide, 
AsH3.  This  may  be  represented  thus  :  — 

AsCl3  +  6  H  =  AsH3  +  3  HC1. 

7.  Characteristics  of  Arsine.  —  This  is  a  colorless,  ex- 
ceedingly poisonous  gas,  which  burns  with  a  pale  violet 
flame,  giving  off  white  fumes  of  the  trioxide  As2O3. 

2  AsH3  +  3  O2  =  As2O3  +  3  H2O. 

Both  of  these  products  may  be  seen  if  a  cold  beaker  or 
test-tube  be  held  over  the  burning  jet  of  arsine.  If  a  cold 
dish  is  held  against  the  flame,  the  temperature  is  lowered 
below  that  required  for  the  combustion  of  arsenic,  and  it 
is  therefore  deposited  in  the  metallic  form,  while  the 
hydrogen  continues  to  burn.  What  does  the  experiment 
teach  regarding  the  kindling  point  of  hydrogen  ? 

8.  The  Oxides  of  Arsenic.  —  Corresponding  to  the  two 
oxides  of  phosphorus  we  have  two  of  arsenic,  the  trioxide, 
As2O3,  and  pentoxide,  As2O5.     Only  the  former  is  of  im- 
portance.     It  occurs  in  two^or  three  forms,  the  white 

being  the  most  common.     It  is  usually  sold  under 


ABSENIC,  ANTIMONY,  BISMUTH  289 

the  name  "  arsenic  "  or  white  arsenic,  but  is  also  called 
arsenious  acid.  It  has  a  sweetish  taste,  is  slightly  soluble 
in  cold  water,  more  so  in  hot,  in  hydrochloric  acid,  and  in 
caustic  soda.  It  is  very  poisonous,  but  acts  somewhat 
slowly.  An  antidote  for  it  is  ferric  hydroxide,  prepared 
by  treating  a  ferric  salt  in  solution  with  ammonia;  the 
precipitate  must  be  filtered  out  and  washed.  Magnesia, 
MgO,  is  also  suggested,  and  is  used  more  often  because  it 
is  to  be  had  already  prepared. 

9.  Arsenic  trioxide  is  used  by  taxidermists  in  curing 
the  skins  of  animals  ;  it  is  an  ingredient  of  many  poisons, 
but  is  also  often  prescribed  by  physicians  as  a  blood  purifier, 
especially  for  removing  facial  eruptions.  It  is  thought  to 
beautify  the  complexion,  and  has  a  tendency  to  produce 
fat.  Because  of  the  latter  property  it  is  sometimes  fed  to 
old  horses  to  prepare  them  for  the  market.  It  stimulates 
the  action  of  the  heart  and  renders  breathing  easier  ;  on 
this  account  it  is  said  to  be  used  by  some  mountain  climb- 
ers. These  apparent  benefits  are  but  temporary,  however, 
and  a  discontinuance  of  its  use  is  attended  by  all  the 
symptoms  of  serious  arsenic  poisoning. 

EXPERIMENT  173.  —  Examine  a  sample  of  arsenic  trioxide  and  note 
its  general  appearances.  Test  its  solubility  in  diluted  hydrochloric 
acid,  also  in  caustic  soda.  Which  is  the  better  solvent?  Use  only 
small  quantities  of  the  trioxide.  Save  the  solution. 

10.  Paris  Green;  Scheele's  Green. — This  is  a  very 
poisonous,  bright  green  powder,  used  often  for  coloring 
and  tinting  and  as  an  insect  exterminator. 

EXPERIMENT  174.  —  Let  the  student  prepare  this  compound,  thus: 
To  a  few  cubic  centimeters  of  a  solution  of  copper  sulphate  in  a 
test-tube  add  ammonia,  drop  by  drop,  until  the  precipitate  which 
forms  at  first  just  dissolves.  Now,  add  gradually  a  solution  of  arsenic ; 
a  bright  green  precipitate  will  form.  If  too  blue,  not  enough  arsenic 


ODERN  CHEMISTRY 


290 


has  been  added.  This  is  one  of  the  easiest  methods  of  detecting 
arsenic  if  present  in  considerable  quantities.  It  is  known  as  Scheete's 
test. 

11.  Arsenic  Trisulphide,  As2S3.  —  This  is  a  bright  yel- 
low powder  obtained  by  passing  a  current  of  hydrogen 
sulphide  through  a  solution  of  arsenic.  It  is  soluble 
in  ammonium  carbonate,  which  distinguishes  it  from  a 
similar  compound  of  tin,  SnS2,  also  yellow.  It  is  also 
soluble  in  yellow  ammonium  sulphide,  but  not  in  hydro- 
chloric acid. 

EXPERIMENT  175.  —  Let  the  student  prepare  this  compound  by 
passing  hydrogen  sulphide  through  a  solution  of  arsenic  trioxide  in 
water  acidulated  with  hydrochloric  acid.  Divide  the  yellow  precipi- 
tate into  two  or  three  parts  and  test  its  solubility  in  hydrochloric  acid 
and  in  ammonium  sulphide  and  carbonate. 

ANTIMONY:  Sb  =  120 

\  12.  Source  of  Antimony.  — This  element  is  found  free  in 
very  small  quantities  only,  but  frequently  occurs  with  the 
ores  of  other  metals,  such  as  lead,  copper,  and  iron.  Its 
principal  ore  is  stibnite,  Sb2S3,  and  from  this  the  commer- 
cial supply  is  obtained. 

13.  Reduction  of  the  Ore.  — There  are  two  methods  used 
for  reducing  antimony  ores.  The  first  consists  in  heating 

the  sulphide  in  a  reverberatory 
furnace,    whereby  the  ore  is 


reduced  to  an  oxide,  thus: — 
Sb2S3+  5  Oa=  SbaO4+-3  SO2. 
Then  the  tetroxide,  tlius 
•formed,  is  mixed  with  char- 
coal, and  again  heated  in  a 
furnace,  when  metallic  antimony  is  obtained,  thus : — 


ARSENIC,  ANTIMONY,  BISMUTH  291 

EXPERIMENT  176.  —  In  a  cavity  in  a  piece  of  charcoal  place  a  little 
antimony  tartrate,  mixed  with  sodium  carbonate,  and  moisten  with 
a  few  drops  of  water.  Now  heat  strongly  with  the  reducing  flame. 
What  do  you  obtain?  Preserve  for  the  next  experiment. 

14.  This  illustrates  the  method  of  reduction  described 
above,  and,  it  will  be  noticed,  is  in  accord  with  the  general 
plan  of  reducing  metallic  ores,  —  first  reducing  them  to 
the  form  of  an  oxide  by  roasting  them,  and  then  deoxi- 
dizing them  by  heating  with  carbon. 

15.  Another  Method.  —  This  consists  in  mixing  the  ore, 
antimony  sulphide,  with  iron,  and  melting  the  whole  in  a 
furnace.     The  iron  combines  with  the  sulphur,  and  pre- 
cipitates the  antimony,  thus  :  — 

Sb2S3  +  3  Fe  =  3  FeS  +  2  Sb. 

16.  Characteristics  of  Antimony. — Owing  to  the  fact 
that,  like  phosphorus,  nitrogen,  and  other  non-metallic  ele- 
ments, antimony  forms  oxides  which  are  the  anhydrides  of 
acids,  it  is  sometimes  regarded  as  a  non-metallic  element. 
It  is,  however,  of  a  highly  lustrous  metallic  appearance, 
steel-gray  in  color,  notably  crystalline  in  structure,  heavy, 
and  so  very  brittle  that  it  is  easily  reduced  to  a  powder. 

17.  Antimony   combines    energetically   with    chlorine, 
bromine,  and  iodine,  in  contact  with  all  of  which,  when 
finely  powdered,  it  quickly  takes  fire.     Upon   bromine, 
sufficient  heat  is  generated  to  melt  the  antimony,  and  it 
spins  around  as  does  sodium  upon  water,  burning  all  the 
time.     At   ordinary   temperatures,    the    metal    does   not 
readily  tarnish  in  the  air,  but  by  means  of  the  oxidizing 
blowpipe  flame  it  is  converted  into  a  white  oxide,  Sb2O3. 
It  is  only  slightly  acted  upon  by  hydrochloric  acid,  but 
nitric  acid  converts  it  into  a  white  powder,   and  it  is 
readily  soluble  in  aqua  regia,  forming  antimony  chloride, 


292  MODERN  CHEMISTRY 

SbCl3.     One  of  its  most  valuable  properties  is  that  of 
expanding  somewhat  upon  solidifying. 

EXPERIMENT  177.  —  To  illustrate  some  of  the  above-mentioned 
properties.  Take  the  metallic  bead  obtained  in  the  preceding  experi- 
ment, and  learn  whether  it  is  magnetic.  Test  it  with  a  hammer  on 
an  anvil  to  learn  whether  it  is  malleable.  Notice  its  color  and  appear- 
ance. Put  a  portion  of  it  on  charcoal  and  try  the  oxidizing  flame. 
What  are  the  results?  How  does  it  differ  from  arsenic  treated  thus? 
Test  the  solubility  of  the  metal  in  nitric  acid;  in  aqua  regia.  State 
results  in  each  case.  Boil  nearly  to  dry  ness  the  latter  solution,  and 
add  water.  What  happens  ?  Treat  this  with  tartaric  acid,  and  state 
results. 

18.  Uses. — Because  of  its  property  of  expanding  when 
it  solidifies,  antimony  is  used  very  extensively  in  mak- 
ing type  metal,  britannia  ware,  and  other  similar  alloys. 
Antimony  may  be  obtained  in  a  powdered  or  amorphous 
condition  by  immersing  a  strip  of  zinc  in  a  solution  of 
some  antimony  salt,  as   the   chloride   or   tartrate.     The 
principle  underlying  is  the  same  as  that  in  the  second 
method   of   reducing   the   ore,    described   already.     This 
antimony  black,  as  it  is  called,  is  a  dark-colored,  finely 
divided  powder,  and  is  sometimes  used  in  giving  plaster 
figures  a  metallic  appearance. 

Compounds  of  Antimony 

19.  There  was  a  time  when  the  compounds  of  antimony 
were  extensively  employed  in  medicine,  but  owing  to  their 
exceedingly  poisonous  character,  their  use  was  prohibited 
by   law,   and    their    applications    now    are    considerably 
limited. 

20.  Stibine,    Antimoniureted    Hydrogen,    SbH3.  —  This 
gas,  known  also  as  hydrogen  antimonide,  corresponding  to 
similar  compounds  of  arsenic  and  phosphorus,  is  usually 


ARSENIC,  ANTIMONY,  BISMUTH  293 

prepared  from  nascent  hydrogen  and  some  antimony  com- 
pound, just  as  arsine  was  prepared  in  Experiment  172. 
It  is  a  combustible  gas,  which  burns  with  a  green  flame, 
and  deposits  upon  a  cold  dish  held  against  this  flame  a 
black  spot  resembling  that  of  arsenic,  but  not  so  lustrous. 
It  is  also  less  volatile  if  heated,  and  is  insoluble  in  a  solu- 
tion of  calcium  or  sodium  hypochlorite. 

EXPERIMENT  178.  —  Prepare  stibine  exactly  as  you  did  the  arsine, 
using  the  same  precautions.  Test  the  spots  with  a  solution  of  bleach- 
ing powder  or  sodium  hypochlorite,  and  verify  the  statements  made 
above. 

21.  Oxides  of  Antimony. — None  of  the  three  oxides  of 
antimony  is  of  any  importance.     The  trioxide,  Sb2O3,  and 
pentoxide,  Sb2O5,  are  the  anhydrides  of  the  acids,  antimo- 
nous  and  antimonic,  corresponding  to  those  of  nitrogen 
from  the  similar  oxides. 

Sb203  +  3  H20  =  2  H3SbO3. 
Sb205  +  3  H20  =  2  H3Sb04. 

22.  The  Chlorides  of  Antimony. — When   antimony  is 
dissolved  in  aqua  regia,  as  in  Experiment  177,  above,  and 
the   solution   evaporated,  antimony  trichloride,   SbCl3,  a 
white  crystalline  salt,  is  obtained.     It  was  formerly  known 
as  "butter  of  antimony,"  from  the  thick  oily  appearance 
which  it  assumes  before  solidifying.     Upon  adding  water 
to  this  compound,  a  white  precipitate  is  formed,  which  is 
known  as  basic  antimony  chloride,  or  antimony  oxychlo- 
ride,  SbOCl.     The  reaction  may  be  expressed  thus  :  — 

SbCl3  +  H20  =  SbOCl  +  2  HC1. 

The  trichloride  has  given  up  two  atoms  of  its  chlorine, 
and  has  taken  in  their  place  one  atom  of  bivalent  oxygen. 


294  MODERN  CHEMISTRY 


This  oxychloride  is  soluble  in  tartaric  acid,  but  not  in 
water. 

23.  Antimony  Trisulphide,  Sb2S3.  —  This  is  obtained  arti- 
ficially by  passing  a  current  of  hydrogen  sulphide  through 
an  antimony  solution.     It  is  of  a  beautiful  orange  color, 
soluble  in  yellow  ammonium  sulphide,  and  also  in  strong 
hydrochloric  acid. 

BISMUTH:   Bi  =  208 

24.  Source  of  Supply.  —  Most  of  the  commercial  supply 
of  bismuth  is  obtained  from  Saxon}'.     It  is  usually  found 
free,  but  alloyed  with  small  quantities  of   several  other 
metals.     It  also  occurs  in  two  ores :  the  sulphide,  Bi2S3, 
known  as  bistnuthite,  and  the  oxide,  Bi2O3. 

25.  Reduction.  —  When  obtained  from  native  bismuth, 
as  it  usually  is,  the  process  consists  of  little  more  than 
simply  heating  to  melt  the  bismuth ;    the  other  metals 
found  with  it  have  a  higher  melting  point,  and  remain 
unchanged.     In  the  case  of  the  ores,  if  bismuthite  is  used, 
it  is  treated  as  the  sulphides  of  other  metals  are,  first  con- 
verted into  an  oxide,  and  then  heated  with  charcoal.     Let 
the   student   write   the    reactions    representing    the    two 
steps. 

26.  Characteristics.  —  Like  antimony,  bismuth  is  a  hard, 
brittle,  distinctly  crystalline  metal.      It  is  steel-gray  in 
color,  having  somewhat  of   a  golden  reflection,  or  upon 
some  surfaces  a  purplish  hue.     It  has  a  low  melting  point, 
being  just  above  tin  in  this  respect,  expands  upon  solidi- 


ARSENIC,  ANTIMONY,  BISMUTH  295 

fying,  and  is  permanent  in -the  air  at  ordinary  tempera- 
tures ;  at  a  red  heat  it  oxidizes  to  a  light  yellow  powder. 
It  unites  readily  with  bromine  and  chlorine,  and  if  sifted 
into  them  takes  tire  at  once. 

EXPERIMENT  179.  —  If  no  bismuth  is  to  be  had  in  the  laboratory, 
prepare  a  little  by  heating  bismuth  nitrate,  mixed  with  sodium  carbo- 
nate ami  moistened,  on  charcoal  with  the  reducing  flame. 

Note  the  color  of  the  metallic  bead;  test  its  hardness  and  mallea- 
bility, and  learn  whether  it  is  magnetic.  Dissolve  a  portion  of  the 
bead  obtained  in  nitric  acid,  boil  nearly  dry,  and  add  water.  What 
forms?  Treat  with  tartaric  acid  in  solution.  Compare  results  with 
similar  tests  with  antimony.  How  do  they  differ? 

27.  Uses.  —  In  the  metallic  form  bismuth  has  but  little 
use,  except  in  alloys.     To  these  it  imparts  the  properties 
of   low  fusing  points  and   of   expansibility.      For  these 
reasons  it  is  used  in  stereotyping,  and  for  similar  purposes 
-where  clearly  defined  copies  are  demanded.     Bismuth  is 
also  used  for  making  safety  plugs  in  boilers,  and  for  very 
fusible  alloys,  sucli  as  Wood's  alloy,  which  melts  at  about 
60°  C. 

EXPERIMENT  180.  —  Put  into  an  iron  spoon  about  2  g.  of  bismuth, 
1  g.  of  lead,  and  1  g.  of  tin,  and  melt  them.  When  cold  put  into  a 
beaker  of  boiling  water.  What  happens  ? 

28.  Most  of  the  bismuth  produced  at  the  smelters  is 
converted  into  its  compounds  and  used  in  a  medicinal  way. 

Compounds  of  Bismuth 

29.  Two  Classes  of  Compounds.  —  Like  antimony,  bis- 
muth forms  two  classes  of  compounds.     These  may  be  rep- 
resented by  the  nitrates  ;  the  ternitrate,  Bi(N  O3)3.  in  which 
it  is  readily  seen  that  the  bismuth  atom  is  tnvalent,  and 
the  basic  nitrate,  BiONO3,  in  which  one  atom  of  oxygen 


296  MODERN  CHEMISTRY 

has   replaced   two   of  the   groups   of   N03.     It  may  be 
graphically  shown  as  follows  :  — 


Ternitrate.  Basic  (Bisniuthyl) . 

30.  The  first  of  these  is  a  white  crystalline  salt,  which 
is  prepared  by  dissolving  metallic  bismuth  in  nitric  acid,, 
It  has  little  use,  except  in  the  preparation  of  other  com- 
pounds of  bismuth.     The  basic  nitrate,  sold  at  drug-stores 
as  the  subnitrate,  or  simply  as    "bismuth,"   is  a  white 
powder,  obtained  from  the  ordinary  nitrate  by  the  addi- 
tion of  water,  whereupon  a  fine  white  precipitate  falls, 
thus :  — 

Bi(NO3)3  +  H20  =  BiONO3  +  2  HNO3, 

or  more  properly,  considering  the  water  of  crystallization, 
Bi(N03)3,  2  H20  +  H20  =  BiON03,  H2O  +  2  HNO8+H2O. 

This  is  used  largely  as  a  cosmetic,  and  for  relieving  the 
irritation  of  chafed  or  chapped  skin ;  also  in  cholera  and 
kindred  diseases,  and  in  acute  dyspepsia. 

31.  Bismuth  Trioxide,  Bi203.  —  This  is  also  called  bis- 
muth ocher,  the  chief  ore  of  bismuth,  but  may  be  obtained 
artificially  by  heating  the  metal  in  the  oxidizing  flame. 
It  is  of  a  deep  yellow  color  when  hot,  but  yellowish  white 
when  cold.     Its  principal  use  is  as  a  paint. 

32.  Bismuth  Trichloride,  BiCl3.  —  This  may  be  prepared 
by  heating  bismuth  in  chlorine  gas.     If  water  is  added 
to  it,  the  basic  bismuth  chloride,  or  oxychloride,  BiOCl, 
is  formed,  as  is  the  case  with  antimony.     The  latter,  how- 


ARSENIC,  ANTIMONY,  BISMUTH 


297 


ever,  is  soluble  in  sodium  tartrate  or  tartaric  acid,  but  the 
former  is  not.  Basic  bismuth  chloride  is  a  fine  white 
powder,  and  is  used  as  a  paint,  known  as  "pearl  white." 
33.  The  Nitrogen  Group.  —  From  the  similarity  of  their 
compounds,  and  their  chemical  affinity,  nitrogen,  phos- 
phorus, arsenic,  antimony,  and  bismuth  are  often  classed 
together  and  called  the  nitrogen  group.  The  following 
table  will  give  a  comparative  view  of  their  more  impor- 
tant compounds :  — 


N=*14 

P  =  31 

As  =  75 

Sb  =  120 

Bi  =  208 

NlTROGEX 

PHOSPHORUS 

ARSENIC 

ANTIMONY 

BISMUTH 

NH3 

PH3 

AsH3 

SbH3 



N,0, 
NA 

P2o3 
PA 

As203 
As205 
AsCl3 

Sb203 
Sb205 
SbCl3 
SbOCl 

Bi203 
Bi205 
BiCl3 
BiOCl 

SUMMARY  OF   CHAPTER 

Comparative  Study  of  Arsenic,  Antimony,  and  Bismuth. 
Sources  of  the  metals. 

Wherein  alike.  Wherein  different. 

Reduction  of  the  ores. 

Wherein  similar  —  How  similar  to  reduction  of  other  metallic 

ores. 

In  what  respects  different. 

Description  of  experiments  illustrating  methods. 
Characteristics  of  the  group. 

Compare  two  of  them  with  the  non-metals. 
Wherein  are  they  all  metallic  in  character. 
Compare  in 

Color.  Melting  point. 

Density.  Tendency  to  oxidize. 

Hardness.  Solubility  in  acids. 

Malleability. 


298  MODERN  CHEMISTRY 

State  any  special  characteristics,  not  common. 

Compare  bismuth   and  antimony  as  to  certain   classes  of  salts 

formed  by  each. 

Compare  arsenic  and  antimony  in  the  same  way. 
Uses  of  each. 

Special  use  for  metallic  arsenic  —  Reason. 
Same  for  antimony,  and  reason. 

Antimony  black  —  How  made?  —  Use? 
Same  for  bismuth,  and  reason. 
Compounds. 

Compare  the  hydrogen  compounds  of  arsenic  and  antimony  as  to 
Method  of  preparing  and  chemical  action. 
Characteristics  of  each. 
How  distinguish  one  from  the  other? 
Products  formed  when  Asll3  burns. 

Experimental  proof. 
Oxygen  compounds. 

Names  and  formulae. 
Important  one  of  arsenic  —  Why  ? 
Appearance  and  uses. 

Physiological  action  —  Compare  with  antimony. 
Antidotes.  Solvents. 

Appearance  and  use  of  bismuth  oxide. 
Sulphides. 

Names  and  formulae. 
Method  of  preparing. 
Appearance  of  each. 
How  distinguish  As2S3from  SnS2? 
How  distinguish  As2S,  from  Sb^? 
How  distinguish  an  antimony  salt  from  one  of  bismuth? 
Special  compounds. 

Paris  green  —  Experimental  preparation. 

Appearar.ce —  Uses. 

Butter  of  antimony  —  Chemical  name  and  formula. 
Means  of  identifying. 

For  arsenic  — Marsh's  test ;  Scheele's  test. 
For  bismuth  and  antimony. 
Comparison  of  the  nitrogen  group. 

Compounds  with  hydrogen,  oxygen,  chlorine,  etc. 


CHAPTER  XXV 

IRON,   NICKEL,   COBALT 
IRON:  Fe  =  56 

1.  Distribution.  —  Iron,  the  most  useful  of  all  metals, 
is  also  the  most  abundant  and  most  widely  distributed. 
It  is  found  in  nearly  all  clays  and  soils,  and  from  these 
is  taken  up  by  plants,  and  through  them  makes  its  way 
into  the  animal  economy.     The  color  of  many  soils,  rocks, 
and  minerals  is  due  to  the  presence  of  iron  in  some  form. 
Pure  iron  does  not  occur  in  any  considerable  quantities, 
except  in  meteorites,  of   which  some   weigh  many  tons. 
The  largest  meteorites  ever  found  were   discovered   by 
Lieutenant    Peary  in  his  Arctic   explorations.      One  of 
these,  weighing  nearly  one  hundred  tons,   was  brought 
back  and  placed  in  the  Brooklyn  Navy  Yard.     Meteorites 
are  found  to  consist  of  iron,  about  93  per  cent,  and  nickel, 
7  per  cent. 

2.  Iron  Ores.  —  A  large  number  of  iron  ores  are  known, 
among  which  are  the  following:  — 

3.  Magnetite,  Fe304.  — This  is  also  known  as  lode-stone, 
on  account  of  its  magnetic  properties. 

4.  Hematite,  Fe.203.  —  This  ore  received  its  name  from 
the  Greek  word    for  Hood,  because  of   the  red  streak  it 
gives   on    porcelain.     It   is   a   very   abundant   ore :    two 
knobs,  Iron  Mountain  and  Pilot  Knob,  of  the  Ozark  Range 
in  Missouri,  consist  almost  entirely  of  hematite,  in  masses 
ranging  all  the  way  from  "the  size  of  a  pigeon's  egg  to 
that  of  a  medium-sized  church." 

299 


300 


MODERN  CHEMISTRY 


5.  Limonite,  2Fe203,  3H20.  —  An  ore  resembling  hema- 
tite, which  gives  a  yellow  streak  on  porcelain. 

6.  Siderite,  FeC03 ;  Spathic  Iron  Ore.  —  This  is  common 
in  some  localities',  has  a  gray  to  brownish  red  color,  and 
often  contains  manganese. 

7.  Iron  Pyrites,  FeS2,  is  a  very  abundant  ore,  but  on 
account  of   the  difficulty  experienced  in  reducing  it,  it 
is  not  used,  except  for  the  manufacture  of  sulphuric  acid. 
It  is  commonly  known  as  "fool's  gold." 

8.  Reduction  of  Ores.  —  This  is  accomplished  in  a  blast 

furnace,  the  essential  features  of 
which  are  shown  in  Figure  61.  The 
furnace  is  from  50  to  75  feet  in 
height,  supported  by  masonry,  and 
strengthened  with  boiler  plate.  It 
is  lined  inside  with  fire-brick.  Near 
the  bottom  some  pipes,  PP,  enter  the 
furnace.  These  are  called  tuyeres,  or 
blast-pipes,  and  furnish  a  powerful 
blast  of  air.  Just  below  these  is  an 
opening,  S,  where  the  slag  is  drawn 
off,  and  below  this  another  opening, 
/,  for  drawing  off  the  iron. 

9.  The  furnace  is  charged  from  the  top  ;  first,  wood  for 
kindling  being  placed  in  the  bottom,  then  alternate  layers 
of  coke  and  iron  ore  mixed  with  limestone.     These  are  all 
dumped  upon  the  cone-shaped  top,  (7,  which  fits  air  tight 
and  works  automatically.     When  the  ore  and  other  mate- 
rials fall  upon  the  top,  it  lowers  mechanically  and  allows 
the  charge  to  roll  into  the  furnace.     Many  of  the  gases 
formed  in  the  interior  of  the  mass  are  combustible,  and 
are  conducted  off  through  the  pipe  M,  and  are  burned  in 
other  furnaces. 


FIG.  61. 


IRCXZV,  NICKEL,   COBALT 


301 


Figure  62  shows  a  perspective  view  of  the  blast  furnace. 
The  various  materials  are  lifted  to  the  top  by  elevators ; 


FIG.  62.  —  Perspective  View  of  Blast  Furnace. 

the  molten  iron  is  drawn  off  and  molded  in  trenches  in 
the  ground  under  the  shed. 


802 


MODERN  CHEMISTRY 


10.  In  accordance  with  the  usual  method  of  reducing 
metallic  ores,  the  oxides  of  iron  are  mixed  with  coke  and 
limestone  and  strongly  heated.     If  an  ore,  not  an  oxide, 
is  used,  it  is  first  calcined  to  convert  it  into  an  oxide. 
The  coke  serves  as  a  deoxidizing  agent,  and  the  lime- 
stone, used  as  a  flux,  is  melted,  and  renders  the  iron  ore 
more    fusible.      The  limestone  then   combines  with   the 
silica  always  present  in  the  ore,  and  forms  a  molten  glass, 
or  slag,  which  floats  upon  the  iron  and  prevents  its  oxida- 
tion by  the  strong  currents  of  air.    The  iron  thus  obtained, 
nevertheless,  absorbs  in  the  intense  heat  of  the  furnace 
considerable  quantities   of   sulphur,  phosphorus,  carbon, 
and  silica,  and  in  this  impure  form  is  not  suited  to  many 
of  the  numerous  demands  for  iron.     From  the  blast  fur- 
nace it  is  run  off  through  trenches  into  molds,  2  to  4  feet 
long,  which  are  called  "pigs,"  and  the  iron  is  known  as 
cast  or  pig  iron.      It  is  very  brittle,  coarse  grained,  and 
contains  from  5  to  10  per  cent  of  impurities. 

11.  Wrought  Iron.  —  This  variety  is  prepared  in  what 
are  known  as  puddling  furnaces.     In  these  the  low  arch- 
ing roof  deflects  the  flames  down- 
ward upon  the  broken  cast  iron. 
The  furnace  is  lined  with  ferric 
oxide,  Fe2O3,  and   as   the  cast 
iron  melts,  the  carbon  which  it 
contains  combines  with  the  oxy- 
gen in  the  lining.     By  stirring 
the  molten  mass,  or  puddling, 
as   it    is   called,   the   whole   is 
gradually  purified,  until  finally, 

as  it  is  much  more  difficult  to  melt  pure  iron,  the  whole 
mass  becomes  pasty.  This  pasty  mass,  bloom,  as  it  is 
called,  is  then  removed  and  hammered  with  trip-hammers, 


FIG.  63. 


IRON,  NICKEL,   COBALT 


303 


a  process  which  drives  out  any  remaining  slag,  and  renders 
the  iron  malleable. 

12.  Steel.  —  Formerly  steel  was   made  from  wrought 
iron  by  embedding  bars  of  the  latter  in  finely  powdered 
charcoal  and  keeping  at  a  red  heat  for  about  ten  days. 
During  this  time  the  bars  of  iron  slowly  absorbed  more 
or  less  carbon,  and  were  converted  into  steel.     Besides 
the   expense   and   the   length   of   time   required   in   this 
process,  there  were  two  other  serious  objections  to  it : 
first,  that  there  was  no  possible  way  of  controlling  accu- 
rately the  amount  of  carbon  taken  up  by  tha  iron,  and 
second,  a  steel  bar  was  obtained  which  was  not  at  all 
uniform  in  quality  and  texture. 

13.  Present  Method  of  Manufacture.  —  At  present,  steel 
is  made  directly  from  cast  iron,  by  the  Bessemer  process. 
An  egg-shaped  vessel,  called  a  converter,  is  used.     It  is 
securely  bound  with  boiler  iron, 

and  is  lined  with  ganister,  a 
siliceous  earth,  fusible  only  at  a 
very  high  temperature.  The 
converter,  which  will  hold  ten 
or  more  tons  of  iron,  is  mounted 
on  axes,  or  trunnions.  One  of 
these,  A,  in  Fig.  64,  is  hollow, 
so  that  a  blast  of  air  may  be 
forced  through  it  when  the 
converter  is  in  a  vertical  posi- 
tion. This  trunnion  opens  into 
a  pipe,  P,  which  extends  down  the  outside  of  the  converter 
and  opens  into  the  tuyere  box,  B,  beneath  the  body  of  the 
converter.  Through  the  tuyere  box,  numerous  small 
openings  admit  the  air  to  the  converter  and  its  con- 
tents. 


FIG.  64.    A  Converter. 


304  MODERN  CHEMISTRY 

14.  Bessemer  Process.  —  About  ten  tons  of  pig  iron  are 
placed  in  a  cupola  furnace,  that  is,  one  resembling  a*  blast 
furnace  in  most  of  its  details,  but  considerably  smaller. 
When  the  iron  is  melted,  it  is  run  into  the  converter. 
Immediately  the  blast  of  air  is  turned  on,  and,  bubbling 
up  through  the  molten  iron,  the  oxygen  unites  with  the 
carbon  and  other  impurities,  burning  them  out.     No  heat 
is  used  in  the  operation  except  what  is  evolved  by  the 
combustion  of  the  impurities  themselves.     About  twenty- 
five  or  thirty  minutes  are  required  for  the  completion  of 
the   operation,    during   most   of   which   time   a   brilliant 
shower  of  sparks  is  thrown  from  the  mouth  of  the  con- 
verter.    This  is  represented  in  colors  by  the  frontispiece. 
The  converter  on  the  right  is  shown  in  action ;  the  one 
on  the  left,  at  the  close  of  the  process,  discharging  the 
molten  steel  into  a  pot,   from  which  it  will  be  poured 
into  molds. 

15.  When  the  mass    of   flame   and   sparks   no   longer 
issues  from  the  converter,  the  workmen  know  that  the 
cast  iron  has  had  its  impurities  entirely  removed,  and  is 
now  wrought  iron.    Next,  a  Aveighed  quantity  of  spiegeleisen 
or  manganese  iron,  containing  a  known  amount  of  carbon, 
is  thrown  into  the  converter,  and  in  a  moment  or  two  the 
process  is  complete.     In  this  way,  in  thirty  minutes  or 
less,  ten  tons  of  steel  are  obtained  at  a  cost  only  a  fraction 
of  what  it  would  be  by  former  methods. 

16.  Basic-lining    Process.  —  If    the    iron   ore    contains 
much    phosphorus,    the    converter    is    lined    with    lime- 
stone, which,  during  the  process  of  oxidation,  takes  up 
the    phosphorus    from    the    iron,   and    is    converted    into 
calcium    phosphate.      This  is  known  as  the  basic-lining 
process  and  was  put  into  practical  use  by  the  inventors, 
Thomas  and  Gilchrist. 


IRON,  NICKEL,   COBALT  305 

17.  Tempering  Steel. — Tempering  consists  in  harden- 
ing steel,  by  heating  and  then  suddenly  plunging  into 
cold  water  or  oil.      Tempered  in  this  way,  it  becomes 
much  less  malleable,  but  can  take  and  hold  a  sharp  edge. 
Different  instruments  require  steel  that  has  been  heated 
to  different  temperatures ;  thus,  surgical  instruments  after 
being  hardened  are  again  heated  to  about  225°  or  till  a 
yellow   film   of   oxide   appears    upon   the   surface.      For 
ordinary  cutlery,  a  temperature  of  about  250°  is  used, 
indicated  by  the  appearance  of  a  brown  film,  while  clock 
and  watch  springs  and  such  forms  as  require  great  elas- 
ticity are  made  of  steel  heated  till  blue,  or  about  290°. 
By  heating  any  form  of  steel  strongly  and  then  cooling 
very  slowly,  the  temper  is  "  drawn,"  or  removed,  and  the 
metal  becomes  like  ordinary  wrought  iron. 

18.  Comparison  of  the  Three  Forms.  — 

CAST  IKON.  STEEL.  WROUGHT  IRON. 

Impurities— 5  to  10%.  1  to  2  %.  0.36  to  0.5  %. 

Brittle.  Somewhat  malleable.  Very  malleable. 

Coarse  grained.  Fine  gf%ined.  Very  fine  grained. 

Cannot  be  tempered.  May  be  tempered.  Cannot  be  tempered. 

Lowest  melting  point.  Medium  melting  point.  Highest  melting  point. 

19.  Uses   of  Iron.  —  This   is   preeminently  the  "  Steel 
Age."     Day  by  day  the  uses  of  iron  are  increasing.     The 
continual  cheapening  of  both  steel  and  wrought  iron  by 
improved  methods  has  caused  their  use  in  thousands  of 
ways  where  wood  was  formerly  demanded.     These  applica- 
tions are  too  well  known,  however,  to  need  mentioning. 

Compounds  of  Iron 

20.  Ferrous  and  Ferric  Compounds.  —  Like  several  other 
metals,  iron  forms  two  general  classes  of  compounds,  the 
ferrous  and  ferric.     The  former  are  very  unstable,  and 


306 


MODERN  CHEMISTRY 


when  exposed  to  the  air  gradually  change  to  the  ferric. 
The  reaction  in  the  presence  of  free  acid  may  be  indicated 
thus  :  — 


2  FeSO4  -h  H2SO4  +  O(air)  =  Fe2(SO4)3 


H2O. 


If  there  is  no  free  acid  present,  a  part  of  the  ferrous  salt 
is  converted  into  the  ferric  and  another  part  into  an 
insoluble  basic  salt. 

EXPERIMENT  181.  —  To  distinguish  between  ferrous  ami  ferric  units. 
Pulverize  a  crystal  of  ferrous  sulphate  and  dissolve  in  a  feu  cubic 
centimeters  of  water;  divide  into  three  portions.  To  one  portion  add 
promptly  a  lew  drops  of  ammonium  hydroxide,  to  the  second  a  few 
drops  of  potassium  sulphocyanide  solution,  to  the  third  a  few  drops  of 
potassium  ferrocvani.le  solution.  Notice  the  results  in  each  case. 
Now  dissolve  a  little  ferric  chloride  or  nitrate  in  water,  divide  into 
three  parts,  and  repeat  the  same  tests.  Compare  results  and  tabulate 
as  below. 


NII4OII 

KSCy 

K4FeCyG 

FeSO, 

Fe.C!G 

EXPKRIMKNT  182.  —  To  show  the  instability  of  ferrous  salts.  Quickly 
dissolve  in  cold  water  a  little  powdered  ferrous  sulphate,  and  divide 
into  two  parts.  To  one  add  a  few  drops  of  ammonium  hydroxide,  and 
note  the  color  of  the  precipitate.  Allow  both  portions  to  stand  for 
some  time.  How  does  the  greenish  precipitate  change  in  color?  Into 
what  is  it  apparently  converted?  Has  the  other  portion  changed  any 
in  appearance?  How?  Test  it  with  potassium  sulphocyanide  or 
ammonia  to  learn  what  kind  of  a  salt  it  is  now.  What  are  your 
conclusions? 

21.  This  experiment  will  show  the  tendency  of  ferrous 
salts.  What  is  thus  accomplished  slowly  by  the  action  of 


IRON,  NICKEL,   COBALT  807 

atmospheric  oxygen  at  ordinary  temperatures  is  effected 
rapidly  by  nitric  acid  at  the  boiling  point.  As  already 
seen,  this  acid  is  a  strong  oxidizing  agent,  readily  giving 
up  a  part  of  its  oxygen  when  heated,  thus  :  — 

2  HN03  +  (heat)  =  H2O  +  2  NO3  +  O. 

This  nascent  oxygen  rapidly  attacks  any  oxidizable 
substance  that  may  be  present.  With  ferrous  chloride 
in  the  presence  of  hydrochloric  acid,  the  following  reaction 
takes  place  :  —  *  **,  f  (s^f  *  #?  °  t^* 


EXPERIMENT  183.  —  To  show  the  effects  of  nitric  acid  upon  a  ferrous 
sail.  Dissolve  a  little  ferrous  sulphate  in  water,  add  a  few  drops  of 
sulphuric  acid  and  then  some  nitric  acid,  and  heat  to  the  boiling  point 
for  two  or  three  minutes.  Does  the  solution  change  any  in  color? 
Now  test  a  part  of  it  in  two  or  three  ways  to  learn  whether  it  has  been 
converted  into  a  ferric  salt.  What  are  your  conclusions? 

22.  Ferric  salts,  on  the  other  hand,  may  be  reduced  to 
the  ferrous  by  treatment  with  hydrogen  sulphide  or  nascent 
hydrogen.     The  reaction  may  be  shown  thus  :  — 

Fe2Cl6  +  H2  =  2  FeCl  +  2  HC1. 
^ 

EXPERIMENT  184. —  To  prove  the  above  statement.  Put  into  a  test- 
tube  about  5  ec.  of  a  solution  of  ferric  chloride  or  nitrate  and  drop  into 
it  a  good-sized  granule  of  zinc.  Now  add  a  little  strong  sulphuric  or 
hydrochloric  acid  to  cause  a  rapid  evolution  of  hydrogen.  In  from  5 
to  7  minutes  the  yellow  color  of  the  ferric  solution  should  have  disap- 
peared. Test  with  ammonia  or  potassium  sulphocyanide.  What  are 
your  conclusions  in  the  matter  ? 

23.  How  to  distinguish  Ferrous  from  Ferric  Salts.  — 
From  the  preceding  work  it  will  be  learned  that  ferrous 
salts  in  solution  are  usually  colorless  or  very  pale  green, 
while  ferric  salts   are   light  brown.      Potassium  sulpho- 


308  MODERN  CHEMISTRY 

cyanide  serves  as  the  most  delicate  method  of  detecting  a 
ferric  salt,  because  even  exceedingly  small  quantities  will 
show  the  characteristic  wine-red  color  ;  with  ferrous  salts, 
however,  it  shows  no  reaction,  hence  will  not  indicate  their 
presence.  Ammonia  gives  precipitates  with  both  classes 
of  salts,  deep  reddish  brown  with  the  ferric,  and  greenish 
with  ferrous.  Potassium  ferrocyanide  and  ferricyanide 
may  also  be  used  to  distinguish  between  the  two. 

24.  Sulphates  of  Iron.  —  Ferrous  sulphate,  FeSO±,  7  N2  0, 
the  only  common  ferrous  salt,  is  formed  when  iron  is  dis- 
solved in  sulphuric  acid.     It  is  commonly  known  as  cop- 
peras or  green  vitriol,  and  occurs  in  light  green  crystals. 
It  is  somewhat  efflorescent,  and  gradually  gives  up  its 
water  of  crystallization,  turning  white  and  breaking  up 
into  a  powder,  anhydrous  ferrous  sulphate.     It  is  used  con- 
siderably in  making  black  ink  and  dyes,  also  as  a  deodorizer 
and  disinfectant. 

EXPERIMENT  185. —  To  show  one  method  of  making  ink.  Prepare  a 
strong  solution  of  ferrous  sulphate,  and  add  to  it  a  little  of  another 
solution  made  by  soaking  some  powdered  nutgalls  in  water.  Notice 
the  bluish  black  color  obtained.  Allow  it  to  stand  a  few  minutes,  and 
notice  whether  the  color  deepens.  Now  add  to  the  solution  a  few 
drops  of  a  solution  of  oxalic  acid.  What  happens?  This  suggests  a 
method  for  removing  ink  stains  without  injuring  the  fiber  of  the  paper 
or  cloth. 

25.  Ferric  Chloride,   Fe2Cl6.  —  This  is  a  brownish  yel- 
low salt,  which  rapidly  absorbs  moisture  when  exposed  to 
the  air.     It  is  obtained  when  iron  is  treated  with  aqua 
regia  or  dissolved  in  hydrochloric  acid  with  the  addition 
of  a  crystal  of  potassium  chlorate.     It  has  little  use  except 
in  the  laboratory. 

26.  The  Sulphides.  —  Ferrous,  FeS ;  Ferric,  .Fe2S3.    The 
former  is  a  dark  gray  substance  somewhat  resembling  cast 


IRON,  NICKEL,   COBALT  309 

iron.  It  is  made  by  fusing  together,  in  the  proportion  of 
their  atomic  weights,  iron  and  sulphur,  and  is  used  exten- 
sively in  the  laboratory  for  making  hydrogen  sulphide. 
Ferric  disulphide  is  the  native  ore,  pyrite,  or  "  fool's  gold." 
It  is  of  a  brassy  yellow  color,  and  frequently  occurs  in 
beautiful  cubes  or  modified  forms  of  the  cube.  It  is  very 
abundant,  but  has  little  use  except  in  the  preparation  of 
sulphur  dioxide  for  the  manufacture  of  sulphuric  acid. 

27.  The  Oxides.  —Ferric,  Fe203.     This  is  met  with  in 
the  ore,  hematite,  already  mentioned.     It  is  also  formed 
when  iron  is  exposed  to  moisture,  and  is  known  as  rust. 
In  the  hydrated  form,  Fe2(OH)6,  ferric  hydroxide,  it  is 
formed  when  any  ferric  solution  is  treated  with  ammonia. 
As  a  reddish  brown  precipitate  it  has  already  been  seen  in 
several  of  the  preceding  experiments.     It  is  sometimes 
used   as   an   antidote   for   arsenic  poisoning.     Magnetite, 
Fe3O4,  is  regarded  as  ferrous  ferrite,  Fe(FeO2)2,  a  salt  of 
ferrous  acid.     Compare  Pb3O4.     The  greenish  precipitate 
obtained  in  some  of  the  preceding  experiments  by  adding 
ammonia   to   a   solution   of   ferrous   sulphate   is    ferrous 
hydroxide,  Fe(OH)2,  or  FeO,  H2O;  that  is,  the  hydrated 
form  of  the  protoxide,  FeO. 

NICKEL:  Ni  =  58.7 

28.  Distribution.  — Like  iron,  nickel  is  never  found  pure 
except  in  meteorites,  of  which,  as  already  stated,  it  often 
constitutes  from  5  to  7  per  cent.     Its  ores  are  fairly  well 
distributed,  but  are  nowhere  in  great  abundance,  and  with 
them  are  always  associated  cobalt  and  iron. 

29.  Characteristics  of  Nickel. — Nickel  is  a  silvery  white 
metal  with  the  faintest  yellow  tinge ;  it  is  susceptible  of  a 
very  high  polish  and  does  not  tarnish  in  the  air.     It  is 


310  MODERN  CHEMISTRY 

very  hard,  melts  at  about  white  heat,  may  be  welded  like 
iron,  is  magnetic,  and  becomes  brittle  like  cast  iron  upon 
the  addition  of  such  impurities  as  cast  iron  always  con- 
tains—  carbon  and  silicon.  Its  density  is  but  little  greater 
than  that  of  iron.  It  is  soluble  in  nitric  acid.  In  most 
respects,  therefore,  it  is  very  similar  to  iron,  and  strikingly 
different  in  one  respect  only. 

30.  Uses.  —  Nickel  is  used  very  extensively  in  alloys, 
among  them  being  certain  coins;  in  gernian  silver,  con- 
sisting of   nickel,  zinc,  and  copper;    and  with  steel  for 
armor  plating  in  making  what  is  known  as  Harveyized 
steel,  noted  for  its  hardness  and  toughness. 

Nickel  is  also  used  largely  in  plating  various  articles  of 
ornament  and  utility. 

31.  Compounds. — The  general  color  of  the  more  com- 
mon i  ickel  salts  is  green.     Among  these  may  be  named 
the  nitrate,  Ni(NO3)2,  chloride,  NiCl2,  sulphate,  NiSO4; 
also  Ni(OH)2,  nickel  hydroxide.      This  last  may  be  pre- 
pared from  a  solution  of  any  of  the  preceding  salts  by 
adding  a  few  drops  of  ammonia  or  caustic  potash. 

EXPERIMENT  186.  —  To  3  or  4  cc.  of  a  solution  of  any  of  the  above 
salts,  add  a  little  caustic  soda.  Describe  the  precipitate  that  forms. 
Te>t  its  solubility  in  hydrochloric  acid.  Write  the  two  reactions 
taking  place. 

32.  A  fifth  compound  which  may  be  mentioned  is  the 
sulphide,  NiS.     It  is  prepared,  as  is  the  sulphide  of  other 
kindred  metals,  by  adding  ammonium  sulphide  to  a  neutral 
or  alkaline  solution  of  any  nickel  salt. 

EXPERIMENT  187.  —  Add  a  little  ammonium  sulphide  to  4  or  5cc. 
of  a  solution  of  any  nickel  salt.  Describe  the  nickel  sulphide  that 
forms.  Test  its  solubility  in  hydrochloric  acid.  Also  in  aqua  regia. 
Write  the  reactions. 


IRON,  NICKEL,   COBALT  311 

33.  Nickel  salts  fused  in  a  borax  bead  impart  to  it  a 
smoky  yellow  or  brown  color  according  to  the  amount  of 
the  nickel  present. 

EXPKRIMEXT  188.  —  Make  a  small  loop  in  the  end  of  a  platinum 
wire,  heat  it  in  the  burner  flame  and  dip  into  some  powdered  borax. 
Kow  hold  again  in  the  flame  until  the  borax  which  swells  up  at  first 
has  formed  a  clear  transparent  glassy  bead.  Dip  into  a  solution  of 
some  nickel  salt,  or  touch  it  to  a  tiny  particle  of  nickel  salt  and  fuse 
again.  If  you  use  the  solution,  it  may  be  necessary  to  dip  the  bead 
several  times.  Note  the  color  imparted. 

EXPERIMENT  183. —  To  fml  ihe  composition  of  a  coin.  Put  a 
"nickel"  into  an  evaporating  dish  and  treat  with  warm  nitric  acid  for 
a  few  minutes.  Remove  the  coin  and  add  a  few  cubic  centimeters  of 
•water.  Pass  a  current  of  hydrogen  sulphide  through  the  solution  for 
several  minutes,  and  filter  out  the  black  precipitate.  After  \\ashing 
it,  punch  a  hole  in  the  bottom  of  the  filter  and  wash  the  precipitate 
through  into  a  beaker  with  a  little  nitric  acid.  Heat  until  it  dissolves. 
What  colored  solution  is  obtained?  What  metal  is  indicated  by  this 
color  ?  Add  ammonia  till  alkaline ;  is  a  deeper  blue  solution  obtained  V 
What  metal  is  it? 

Boil  nearly  to  dryness  the  filtrate  from  the  black  precipitate  above ; 
note  the  color.  Does  this  indicate  any  salts  with  which  you  are 
familiar?  Make  a  borax  bead  as  directed  in  the  preceding  section 
and  test  the  solution  ;  what  are  your  conclusions? 

Of  what  two  metals  is  the  coin  composed?  If  you  can  obtain  one 
of  the  lighter-colored  pennies  seen  occasionally,  test  it  in  the  same 
way. 

COBALT:  Co  =  59 

34.  Characteristics.  —  This  is  a  somewhat  rare  metal  that 
is  usually  found  associated  with  nickel.     It  is  very  similar 
to  iron  and  nickel  in  its  characteristics,  being  steel-gray  in 
color,  very  hard,  magnetic,  and  of  about  the  same  melting 
point.     It  is  permanent  in  the  air.     The  metal  itself  has 
no  application  in  any  of  the  arts. 

35.  Compounds.  —  Cobalt   forms  salts   with   the   three 
common  acids ;    the  nitrate,  Co(NO3)3  ;  cJiloridt,  CoCl3 ; 


312  MODERN  CHEMISTRY 

and  sulphate,  CoSO4.  These  are  all  some  shade  of  red 
in  color,  but  when  heated  so  as  to  lose  their  water  of 
crystallization  they  become  blue. 

36.  The  hydroxide  and  sulphide  are  prepared  just  as  the 
similar  compounds  of  nickel  are. 

EXPERIMENT  190.  —  Prepare  the  last  two  as  you  did  the  correspond- 
ing compounds  of  nickel  in  Experiments  186  and  187,  and  test  their 
solubility  in  the  same  way. 

37.  None  of  the  above  has  much  use  except  occasionally 
in  the  laboratory.     There  are  one  or  two  others,  however, 
which  have  extensive  application  in  the   arts.      Among 
these  may  be  named 

38.  Smalt,  a  silicate  of  cobalt.     When  fused  with  glass 
or  pottery  ware  this  imparts  a  beautiful  blue  color,  and  is 
largely  used  for  that  purpose.     It  may  be  illustrated  in  the 
following  experiment  :  — 

EXPERIMENT  191.  —  Prepare  a  borax  bead  as  you  did  for  nickel, 
and  fuse  with  it  some  salt  of  cobalt.  Note  the  color  imparted.  If  it 
is  too  dark  to  recognize,  it  is  because  too  much  cobalt  has  been  intro- 
duced. Break  out  the  bead,  and  repeat  the  experiment,  using  less  of 
the  compound. 

39.  Sympathetic  Inks.  —  They  are  inks   which   under 
ordinary  circumstances  are  invisible,  or  nearly  so,  on  paper  ; 
when  heated  or  treated  by  some  other  method  they  become 
legible.     Many  of  these  have  some  compound  of  cobalt  as 
their  basis. 

EXPERIMENT  192.  —  Mix  a  solution  of  some  compound  of  cobalt 
with  one  of  ferrous  sulphate.  Using  this  as  an  ink,  write  with  it  upon 
paper,  and  when  the  inscription  is  dry  heat  it.  Do  you  obtain  a  dis- 
tinct green  color,  though  before  it  was  nearly  invisible  ?  In  the  same 
way  try  potassium  iodide  mixed  with  the  cobalt  solution.  Results? 


IKON,   NICKEL,   COBALT  313 

SUMMARY  OF  CHAPTER 

Iron,  Nickel,  Cobalt. 

Occurrence  —  Wherein  are  iron  and  nickel  similar. 

History  of  some  large  meteorites. 

Some  important  ores  of  iron. 
Names  and  formulae. 
Localities  where  found. 
Reduction  of  iron  ores  —  Description  of  blast  furnace. 

Drawing  of  essential  features. 

Method  of  charging  the  furnace. 

Chemical  action  that  takes  place. 

Plan  of  molding  pig  iron. 
Varieties  of  iron  —  Three. 

How  different  in  composition  and  properties  ? 

Description  of  the  puddling  furnace. 
Chemical  action. 

Meaning  of  term  bloom. 

Description  of  the  converter. 

Explanation  of  the  chemical  changes. 

Plans  used  for  phosphorus-bearing  iron  ores. 
Tempering  steel. 

Meaning  of  the  term. 

Process  used. 
Characteristics  —  Compare  iron  and  nickel  as  to 

Color.  Susceptibility  of  polish. 

Hardness.  Permanency  in  the  air. 

Melting  point.  Several  other  similarities. 

Magnetic  properties. 

Uses  —  Compare  nickel  and  iron.  ' 

Compounds  —  Classes  of  iron  compounds. 

Compare  them  as  to  stability. 

Plans  for  distinguishing  the  two. 

Method  of  converting  each  into  the  other.     Explain 
the  chemical  action  in  each  case. 

Names  of  three  or  four  compounds  of  iron  and  their 
uses. 

Compare  the  compounds  of  nickel  and  cobalt  in  color 
and  method  of  preparation. 


CHAPTER  XXVI 

THE  PLATINUM  GROUP 

PLATINUM  :  Pt  =  195 

1.  Where  obtained.  —  Platinum  is  a  rare  metal,  usually 
found  uncombined,    but   almost   always   associated   with 
iridium,  and  smaller  quantities  of  palladium  and  osmium. 
The  greater  portion  of  the  commercial  supply  comes  from 
the  Ural  Mountains  in  Russia,   though  small   quantities 
have  been  obtained  in  California,  Arizona,  and  some  parts 
of  South  America. 

2.  Characteristics.  —  Platinum  is  a  hard,  silvery  white 
metal,  unaffected  by  the  air  at  any  temperature.      It  is 
somewhat  malleable,  but  becomes  less  so  if  alloyed  with  a 
small  per  cent  of  iridium,  though  by  this  means  its  hard- 
ness is  increased.     It  is  a  very  dense  metal,  with  a  specific 
gravity  of  21.5,  -osmium,  the  heaviest  metal  known,  having 
a  density  of  only  22.5.     The  melting  point  of  platinum  is 
about  1900°  C.,  and  it  can  be  fused  only  by  such  intense 
heat  as  that  of  the  oxyhydrogen  blowpipe,  or  acetylene 
blast  lamp.      Like  gold,  it  is  soluble  only  in  nitre-hydro- 
chloric acid,  forming  therewith  platinic  chloride,  PtCl4. 

3.  Property  of  occluding  Gases.  —  The  most  remarkable 
property  of  platinum  is  that  of  occluding  or  absorbing 
various  gases  within  its  pores.     It  is  estimated  that  at 
ordinary  temperatures  it  will  absorb  200  times  its   own 
volume  of  oxygen.    In  the  spongy  form,  that  is,  when  finely 
divided,  as  in  the  case  of  a  metallic  precipitate,  the  power  of 

314 


THE  PLATINUM  GROUP  315 

absorption  is  especially  striking.  If  a  current  of  hydrogen 
be  directed  against  the  platinum  sponge,  so  rapid  will  be 
the  absorption  that  almost  instantly  the  metal  will  become 
red  hot,  and  in  two  or  three  seconds  the  jet  will  be  ignited. 

EXPERIMENT  193.  —  Repeat  Experiment  23  with  hydrogen. 

4.  If  into  ajar  of  hydrogen  and  oxygen,  mixed  in  the 
proportion  of  two  to  one,  a  platinum  sponge  be  introduced, 
the  gases  will  be  made  to  unite  with  explosive  violence. 
This  power  of  occlusion  may  be  seen  in  the  case  of  certain 
other  gases,  as  ammonia  and  common  coal  gas. 

EXPERIMENT  19i.  —  Support  upon  a  ring-stand  a  small  flask  con- 
taining some  strong  aqua  ammonia;  warm  it  gently  so  as  to  secure  a 
constant  and  rapid  evolution  of  gas  from  the  liquid.  Now  heat  to 
bright  redness  in  the  Buusen  flame  a  spiral  of  platinum  wire,  made 
by  coiling  it  about  a  small  glass  rod,  and  hold  it  in  the  neck  of  the 
flask.  The  wire  will  continue  to  glow,  and  the  intensity  of  the  heat 
will  often  be  increased. 

Take  this  same  platinum  coil  and  flatten  it  a  little  so  as  to  bring  the 
parts  of  the  spiral  closer  together;  hold  it  in  the  Bunsen  flame  until 
red  hot,  then  turn  off  the  gas.  When  the  redness  has  just  disappeared 
from  the  wire,  again  turn  on  the  gas.  The  wire  will  quickly  grow  red 
again,  and  in  two  or  three  seconds  will  re-ignite  the  escaping  gas. 
This  may  be  repeated  over  and  over  again.  The  same  may  be  tried 
with  a  spirit  lamp. 

5.  Platinum    Alloys. — Platinum    readily   alloys   with 
lead,  silver,  antimony,  and  other  metals  which  are  easily 
reduced  from  their  compounds  ;  hence  it  should  never  be 
strongly  heated  in  contact   with   them.     It   is    likewise 
injured  by  heating  in  a  smoky  flame,  or  by  placing  upon 
red-hot  charcoal,   which  blisters  the  surface.     Platinum 
vessels  are  usually  cleaned  by  fusing  in  them  for  a  few 
minutes  some  acid  potassium  sulphate,  KHSO4,  and  are 
polished  by  rubbing  gently  with  a  little  fine  sea-sand. 


316  MODERN  CHEMISTRY 

6.  Uses.  —  The  rarity  of  the  metal  and  the  long,  com- 
plicated processes  involved  in  preparing  it  in  the  pure 
form,  make  it  almost  as  expensive  as  gold.  It  is  worth 
from  50  cents  to  75  cents  per  gram,  or  about  $300  per 
pound.  It  is  made  into  wire,  foil,  and  various  articles 
for  use  in  the  chemical  laboratory,  such  as  crucibles, 
dishes,  tips  of  forceps,  etc.  To  the  chemist  it  is  simply 
indispensable  in  analytical  work. 

SUMMARY   OF  CHAPTER 

Names  of  the  elements  in  this  group. 
Source  of  the  supply  of  platinum. 
Characteristics  of  platinum. 

Experiments  that  illustrate  these. 
Alloys  of  platinum. 
Uses  and  value  of  the  metal. 
Compare  with  metals  studied  previously  as  to 

Color. 

Melting  point. 

Density. 

Tendency  to  oxidize. 

Power  of  occluding  gases. 

Solubility  in  acids. 


CHAPTER  XXVII 

CHROMIUM  AND  ITS  COMPOUNDS 
CHROMIUM  :  Cr  =  52 

1.  Where  found.  —  Chromium  is   a   rare   metal  which 
received  its  name  from  the  Greek  word,  chromos,  meaning 
color,  and  is  so  named  because  of  the  striking  colors  of 
most   chromium   compounds.      It   occurs   chiefly   in   the 
Shetland  Islands  in  the  form  of  chromite,  or  chrome  iron, 
Cr2O3,  FeO,  also  written  FeCr2O4.      It  is  also  found  as 
crocosite,  PbCrO4,  in  Siberia,  Brazil,  and  the  Philippine 
Islands. 

Compounds  of  Chromium 

2.  Classes.  —  In  the  metallic  form  chromium  has  but 
little  use.     Its  compounds,  however,  have  various  applica- 
tions.    They  may  be  divided  into  two  important  classes : 

3.  Chromium  as  a  Basic  Element.  —  Those  in  which 
chromium   acts  as  a  basic  element,  with   the   power  of 
replacing  the  hydrogen  in  acids  to  form  salts.     Of  these, 
as  in  the  case  of  iron,  mercury,  and  others,  there  are  two 
divisions,  the  chromous  and  chromic,  but  only  the  latter 
are  important.     As  examples,  we  have  chromic  chloride, 
CrCl3,  chromic  nitrate,  Cr(NO3)3,  and  chromic  sulphate, 
Cr2(SO4)3.     These  as  a  rule  are  green  in  color,  but  the 
double  sulphate  of  potassium  and  chromium,  K2Cr2(SO4)4, 
is  violet.     Solutions  of  the  chromic  salts  are  precipitated 
by   caustic   potash   or   ammonia,   giving   the   hydroxide, 
Cr(OH)3. 

317 


818  MODERN  CHEMISTRY 

4.  Chromium  as  an  Acid  Producer.  —  Those   in  which 
chromium  serves  as  a  noil-metallic  element,  forming  acids. 
Of  these  there  are  three  classes,  but  only  two  merit  notice, 
the  chromates  and  the  die hro mates.      The  chronmtes  are 
based  on  the  theoretical  chromic  acid,  H2CrO4,  wherein 
the  chromium  atom  is  that  which  distinguishes  the  acid,  as 
does  the  sulphur  in  sulphuric  acid,  H2SO4.     The  general 
color  of  the  chromates  is  yellow,  though  there  are  some 
exceptions.     The  best-known  example  is  potassium  chro- 
mate,  K2CrO4. 

EXPERIMENT  195.  —  To  prepare  some  other  chromates.  To  3  or  4  cc. 
of  a  solution  of  potassium  chromate  in  a  test-tube  add  a  few  drops  of 
lead  nitrate  or  acetate  in  solution.  Notice  the  color  of  the  lead  chro- 
mate formed.  In  the  same  way  prepare  some  barium  chromate  by  us- 
ing barium  chloride  with  the  potassium  chromate.  Compare  its  color 
with  the  preceding.  Now  prepare  some  silver  ehromate  by  using  silver 
nitrate  solution  with  the  potassium  chromate.  Note  its  appearance. 

5.  Potassium  Bichromate,  K2Cr2Or  orange-red  in  color, 
is  the  best-known  example  of  the  dichromates. 

Tabular  view  of  the  compounds :  — 
I.    Chromium  as  a  true  metal :  — 

1.  Chromous. 

2.  Chromic  — 

a.  Chloride,  CrCl3. 

b.  Nitrate,     Cr(NO3)3. 

c.  Sulphate,  Cr2(SO4)3. 

II.    Chromium  as  an  acid  former  :  — 

1.  Chromates  — 

a.  Potassium,  K2Cr04. 

b.  Lead,  PbCrO4. 

c.  Barium,       BaCrO4. 

2.  Dichromates  — 

a.   Potassium,  K2Cr2O7. 


CHROMIUM  AND  ITS  COMPOUNDS  319 

6.  Conversion  of  Ons  Class  of  Compounds  into  Another.  — 
Though  the  chromium  salts  are  stable,  they  may  easily  be 
converted  from  one  into  another.     By  adding  a  little  acid 
and  passing  a  current  of  hydrogen  sulphide  through  a 
solution  of  potassium  chromate,  the  latter  is  changed  into 
a  salt  of  the  first  class  (chromic).     The  change  of  color- 
to  green  indicates  that  the  reduction  has  taken  place;  at 
the  same  time  free  sulphur  is  precipitated.     Thus  :  — 

2  KaCr04  +  3  H2S  +  10  HC1  =  4  KC1  +  2  CrCl, 

+  8  H2O  +  3  S. 

EXPERIMENT  196.  To  prove  the  above.  —  Put  into  a  test-tube  a 
few  cubic  centimeters  of  a  solution  of  potassium  eliminate,  and  add 
a  little  hydrochloric  acid.  Now  pass  through  the  solution  a  current 
of  hydrogen  sulphide.  What  change  in  color  is  noticed?  Is  the 
sulphur  precipitated? 

7.  Sulphur  dioxide  has  a  like  reducing  effect  upon  a 
chromate  solution. 

EXPERIMENT  197.  —  Put  into  a  test-tube  4  or  5  cc.  of  a  solution  of 
sodium  sulphite,  Na2S03,  and  a  little  hydrochloric  or  sulphuric  acid. 
Notice  that  sulphur  dioxide  gas  is  being  liberated.  Now  add  a  little 
potassium  chromate  or  dichroinate.  How  does  the  chromium  solution 
change  in  color?  If  sodium  sulphite  is  not  to  be  had,  fill  a  bottle  with 
sulphur  dioxide  gas,  pour  in  the  dichromate,  and  shake. 

EXPERIMENT  193.  To  show  the  reduction  of  the  Hlchromnles  to  the 
chromic  sail*.  —  Put  into  an  evaporating  dish  10  or  15  cc.  of  a  solution 
of  potassium  dichromate,  add  some  hydrochloric  acid,  and  boil  a  few 
minutes.  The  addition  of  a  little  alcohol  will  hasten  the  action. 
Notice  the  change  in  color.  What  compound  of  chromium  is  probably 
formed? 

8.  The  above  experiments  prove  that  either  the  chro- 
mates  or  dichromates  may  be  reduced  to  salts  of  the  first 
class.     The  reaction  that  takes  place  in  the  latter  is  as 
follows :  — 

KaCrs07  +  14  HC1  =  2  KC1  +  2  CrCl3  +  7  H2O  +  6  CL 


320  MODERN  CHEMISTRY 

EXPERIMENT  199.  —  To  2  or  3  cc.  of  potassium  chromate  solution 
in  a  test-tube  add  a  few  drops  of  hydrochloric  or  nitric  acid.  How 
does  its  color  change  ?  What  other  salt  of  chromium  in  solution  does 
it  resemble  ?  In  like  manner  treat  2  or  3  cc.  of  potassium  dichromate 
solution  with  a  few  drops  of  caustic  potash  or  any  alkali.  Notice  the 
change  in  color ;  what  chemical  change  has  taken  place  ? 

9.  It  will  be  seen  by  the  above  experiments  that  the 
chromates  and  dichromates  may  readily  be  converted,  the 
one  into  the  other.  The  reactions  taking  place  are  shown 
thus :  — 

2  K2Cr04  +  2  HC1  =  K2Cr2O7  +  2  KC1  +  H2O, 
and          K2Cr2O7  +  2  KOH  =  2  K2CrO4  +  H2O. 

10.  The  Oxides  of  Chromium.  —  Or*  0*  and  Or  0»,  chro- 

&       o  o~ 

mium  sesquioxide  and  trioxide.  The  former  is  basic  in 
properties,  the  latter  acid.  The  former  is  green,  and  is 
used  in  imparting  a  green  color  to  glass  and  enamel ;  the 
latter  is  a  dark  red  crystalline  solid. 

EXPERIMENT  200.  —  Make  a  borax  bead  and  dip  it  into  a  solution 
of  some  chromium  salt,  then  fuse  in  the  burner  flame.  If  a  good  color 
is  not  secured  the  first  time,  repeat  the  operation. 

11.  Chromium   trioxide   may  be   prepared   by  adding 
strong   sulphuric   acid   to  a  saturated  solution  of   potas- 
sium dichromate.     After  standing  for  some  time,  beautiful 
red  needle-like  crystals  separate  from  the  liquid,  thus:  — 

K2Cr2O7  +  H2SO4  =  2  CrO3  +  KaSO4  +  H2O. 

These  cannot  be  filtered  out  by  ordinary  methods,  as  the 
trioxide  is  a  strong  oxidizing  agent  and  readily  gives  up  a 
part  of  its  oxygen  to  any  organic  compound,  itself  being 
changed  into  the  sesquioxide,  thus  :  — 

2CrO3=Cr2O3  +  3O. 


CHROMIUM  AND  ITS  COMPOUNDS  321 

12.  Chromium  trioxide  is  theoretically  the  anhydride 
of  chromic  acid,  H2CrO4,  and  seemingly  ought  to  produce 
it  when  added  to  water,  thus  :  — 

CrO3  +  H20  =  H2Cr04. 

But  the  action  is  merely  one  of  solution,  and  the  acid  is 
not  formed. 

13.  Chromic  Hydroxide,   Cr(OH)3.  —  This   is   a   green 
precipitate  formed  when  ammonia  or  caustic   potash   is 
added  to  any  chromic  salt,  as  the  chloride  or  sulphate. 

CrCl3  +  3  KOH  =  Cr(OH)3  +  3  KC1. 

14.  Uses  of  the  Compounds.  —  Some  of  the  uses  of  chro- 
mium compounds,  among  others  those  of  the  sesquioxide 
and  of  lead  chromate,  have  been  mentioned.      Both  the 
chromate  and  dichromate  of  potassium  are  used  as  reagents 
in  the  laboratory,  and  in  the  arts  for  dyeing  and  calico 
printing.     If  the  reaction, 

K2Cr2O7  +  8  HC1  =  2  KC1  +  2  CrCl3  +  4  H2O  +  3  O, 

is  studied,  it  will  be  seen  that  potassium  dichromate,  treated 
with  hydrochloric  acid,  is  a  strong  oxidizing  agent.  Each 
molecule  gives  up  three  atoms  of  oxygen.  If  no  other  salt 
is  present,  this  nascent  oxygen  unites  with  the  hydrogen 
in  six  additional  molecules  of  hydrochloric  acid,  thus  :  — 

6  HC1  +  30  =  3  H20  +  6  Cl. 

Combining  the  last  two  reactions,  it  will  be  seen  that  we 
have  the  one  given  on  page  319,  showing  the  reduction  of 
potassium  dichromate  to  chromic  chloride.  However,  if 
any  oxidizable  salt  be  present,  as,  for  example,  a  ferrous 
compound,  the  nascent  oxygen  readily  converts  it  from 


322  MODERN  CHEMISTRY 

\ 

the  ferrous  to  the  ferric  condition.  This  is  shown  in  the 
following  reaction  :  — 

2  FeCl2  +  2  HC1  +  O  =  Fe2Cl6  +  H2O. 

On  account  of  this  property,  potassium  dichromate  is  fre- 
quently used  by  chemists  in  estimating  the  amount  of  iron 
present  in  a  solution. 

EXPERIMENT  201.  —  To  illustrate  this  use  and  the  oxidizing  power 
of  potassium  dichromate.  Dissolve  a  little  ferrous  sulphate  in  a  few 
cubic  centimeters  of  water  and  add  some  hydrochloric  acid.  Now 
add  gradually  drop  by  drop  a  solution  of  potassium  dichromate. 
Notice  how  the  solution  changes  to  green.  Test  a  portion  of  it  with 
potassium  sulphocyanide  and  learn  whether  the  solution  has  been 
oxidized  to  the  ferric  condition.  What  are  your  conclusions?  Study 
some  of  the  foregoing  reactions  and  see  whether  you  can  determine 
why  the  solution  became  green. 

SUMMARY  OF  CHAPTER 

Origin  of  the  term  chromium.    Why  applied  to  this  metal. 
Classification  of  the  chromium  compounds. 

Names  and  formulae  of  the  most  important. 
Relation  of  the  classes  of  compounds. 

Method  of  converting  those  of  second  class  to  first. 

Indication  of  the  change. 

Method  of  converting  chromates  into  dichromates,  and  vice 

versa. 
Compare  the  two  oxides  in 

Appearance. 

Properties. 
Commercial  uses  of  certain  compounds. 

Chromium  sesquioxide. 

Chrome  yellow. 
Laboratory  uses. 

What  uses  as  a  reagent. 

How  used  as  an  oxidizing  agent. 

Experiment  to  illustrate. 


CHAPTER  XXVIII 

MANGANESE  AND  ITS  COMPOUNDS 

MANGANESE  :  Mn  =  55 

1.  Where  found. — This  is  a  somewhat  rare  metal,  often 
associated  with  iron  ores.      The  most  abundant  natural 
compound  is  the  dioxide,  MnO2,  known  as  pyrolusite.     In 
the  metallic  form,  manganese  has  little  use,  but  some  of  its 
compounds  are  valuable. 

Compounds  of  Manganese 

2.  Classes.  —  These  may  be  classified  as  follows  :  — 

3.  As  a  Metal.  —  Those  in  which  manganese  acts  as 
a  metal,  that  is,  having  the  power  of  replacing  hydrogen 
in  acids.     These  may  be  divided  into 

a.  Manganous, 

b.  Manganic, 

of  which  only  the  former  are  important.  The  most  com- 
mon of  these  are  manganous  chloride,  MnCl2,  and  manganous 
sulphate,  MnSO4,  both  crystalline  salts,  pink  in  color. 
From  these  may  be  prepared  the  hydroxide,  Mn(OH)2, 
by  adding  ammonia  to  a  solution  of  either  salt ;  also  the 
sulphide,  MnS,  by  adding  ammonium  sulphide. 

EXPERIMENT  202.  —  Using  a  solution  of  either  manganous  chloride 
or  sulphate,  prepare  the  hydroxide  and  sulphide  as  indicated  above 
and  describe  their  appearance.  Test  their  solubility  in  hydrochloric 
acid.  State  results. 

323 


324  MODERN  CHEMISTRY 

4.  Manganese  Dioxide.  —  In  this  connection  we  shall 
notice  the  most  important  of  the  oxides,  MnO2,  man- 
ganese dioxide.  It  is  a  black  compound,  and  is  used  in  pre- 
paring oxygen,  bromine,  chlorine,  and  iodine.  Notice  the 
similarity  in  method  of  the  last  three. 


MnO2  +  2  NaCl  +  2  H2SO4  =  C12  +  MnSO4  +  Na2SO4  +  2  H2O 
"       =Br2+      "       +       "       +     " 
"       =L    +      "       +       "       +      " 


Cl 
Br 
I 

5.  As  an  Acid  Former.  —  Compounds  in  which  man- 
ganese serves  as  an  acid-forming  element.    Of  these,  there 
are  two  classes, 

a.  Manganates, 

b.  Permanganates. 

The  first  of  these  is  based  upon  a  theoretical  acid,  man* 
ganic,  H2MnO4 ;  they  are  not  of  special  interest  to  us.  The 
best-known  example  of  the  second  is  potassium  perman- 
ganate, KMnO4. 

6.  Potassium  Permanganate.  —  This  is  a  dark  purple 
crystalline  salt,  soluble  in  water.     It  is  used  frequently  in 
the  laboratory  as  a  reagent,  in  a  technical  way  for  the 
estimation  of  iron  in  iron  ores,  and  for  the  testing  and 
purification  of  cistern  water.     Like  nitric  acid  and  potas- 
sium dichromate  (see  pages  88,  321),  it  is  a  strong  oxidizing 
agent.    When  treated  with  hydrochloric  or  sulphuric  acid, 
it  gives  up  oxygen,  thus  :  — 


2  KMnO4+3  H2SO4=K2SO4  +  2  MnSO4+3  H2O  +  5  O. 

The  nascent  oxygen  thus  obtained  may  be  used  in  oxidiz- 
ing ferrous  salts  to  the  ferric  condition,  or  in  destroying 


MANGANESE  AND  ITS  COMPOUNDS  325 

(oxidizing)  the  organic  matter  contained  in  a  solution. 
In  the  case  of  the  iron  the  reaction  may  be  shown  thus  :  — 

10  FeSO4  +  8  H2S04  +  2  KMnO4 

=  K2SO4  +  2  MnSO4  +  5  Fe2(SO4)8  +  8  H2O ; 

or,  the  five  atoms  of  oxygen  set  free  as  shown  above  de- 
compose five  additional  molecules  of  sulphuric  acid,  thus :  — 

5  O  +  5  H2S04  =  5  H20  +  —  (SO4)6. 

Then  the  five  (SO4)  groups  or  ions  unite  with  the  10FeSO4, 
forming  the  ferric  salt,  5  Fe2(SO4)3.  Sometimes  it  is 
written  thus :  — 

10  FeO  +  5  O  =  5  Fe2O3, 

which  expresses  in  a  simple  form  the  same  change  from  a 
ferrous  to  a  ferric  condition. 

EXPERIMENT  203.  —  To  show  the  oxidizing  power  of  potassium  per- 
manganate. To  a  fresh  solution  of  ferrous  sulphate  add  one  or  two 
cubic  centimeters  of  sulphuric  acid,  and  then  slowly,  drop  by  drop, 
potassium  permanganate  until  the  solution  just  begins  to  turn  pink. 
Now  test  it  with  potassium  sulphocyauide  or  ammonium  hydroxide. 
Have  you  obtained  a  ferric  salt?  In  this  connection  study  the  preced- 
ing reactions. 

In  the  same  way  test  some  cistern  water  that  has  an  offensive  odor. 
Before  adding  the  permanganate  heat  the  water  nearly  to  boiling. 
Does  it  lose  its  odor  by  this  treatment  ?  In  the  same  way  try  some 
cistern  water  discolored  with  cedar  shingles;  is  the  color  removed? 
Try  also  a  strong  solution  of  logwood;  can  you  remove  the  dark  color? 

What  instances  can  you  give  in  which  nitric  acid  has  served  as  an 
oxidizing  agent  ?  Potassium  dichromate  ? 

7.  The  sulphuric  acid  is  added  simply  to  dissolve  a  dark- 
colored  precipitate  that  would  otherwise  form  and  obscure 
the  results.  In  purifying  cisterns,  of  course  the  acid  can- 
not be  used,  but  the  brown  solid  in  a  short  time  settles  to 
the  bottom  and  remains  there.  The  amount  of  organic 


326 


MODERN  CHEMISTRY 


matter  in  cistern  water  may  be  learned  by  measuring  the 
amount  of  potassium  permanganate  added  before  the  water 
begins  to  turn  pink.  Sometimes  a  manganese  solution  or 
salt  is  proved  by  the  color  it  imparts  to  the  borax  bead. 

EXPERIMENT  204.  —  Prepare  a  bead  as  in  the  case  of  nickel  or 
cobalt,  and  fuse  with  some  salt  of  manganese.  Notice  the  beautiful 
color  imparted. 

SUMMARY  OF  COMPOUNDS 


Class  I 

A  true  metal  in 
its  chemism. 


Class  II 
An  acid-forming  -j  2. 
element. 


a.  Chloride,  MnCl2. 

b.  Sulphate,  MnSO4. 

1.  Manganous     c.    Hydroxide, 

Mn(OH)2. 
d.   Sulphide,  MnS. 

2.  Manganic,  Dioxide,  MnO2. 
1.    Manganates,  not  important. 

Permanganates,  Potassium, 
KMnO4. 

Compare  the  above  compounds  with  those  of  chromium 
and  note  the  few  differences. 


SUMMARY  OF   CHAPTER 

Occurrence  of  manganese. 

How  associated.  Chief  ore. 

Classification  of  its  compounds. 

Compare  with  the  compounds  of  chromium,  showing  wherein 

similar  and  wherein  different. 
Uses  of  certain  compounds. 
Manganese  dioxide. 
Appearance. 
What  laboratory  uses. 
What  commercial  uses. 
Potassium  permanganate. 
Appearance. 

Laboratory  uses.     Experiments  to  illustrate. 
Practical  uses.    Experiment  to  illustrate. 


APPENDIX  A 


QUALITATIVE  ANALYSIS 

IT  is  not  intended  in  the  following  pages  to  give  any- 
thing like  a  complete  system  of  qualitative  analysis.  Such 
would  be  impossible,  keeping  within  the  necessary  bounds 
of  a  high-school  text.  As  a  matter  of  reference,  however, 
and  to  meet  the  demand  of  any  who  may  care  to  pursue 
to  some  extent  this  line  of  work,  the  following  brief 
outline  is  offered. 

The  student  has  noticed  already  that  a  reagent  which 
will  precipitate  some  metals  from  their  solutions  may  have 
no  effect  upon  various  other  metals.  Taking  advantage 
of  this  fact,  we  are  able  to  divide  the  metals  into  groups, 
and  then  to  separate  the  members  of  these  groups  one  from 
another.  Accordingly,  depending  upon  the.  reagents  used 
for  precipitating  the  metals,  five  divisions  are  usually 
made  as  follows  :  — 


Group  I 


Group  II 


1.  Lead 

2.  Mercury 
(ous  salts) 

3.  Silver 
Antimony 
Tin 

Arsenic 
Mercury 

(ic  salts) 
Copper 
Bismuth 
Cadmium 


Precipitated  as  chlorides, 
PbCl2,  Hg2Cl2,  AgCl, 
by  using  hydrochloric  acid. 

Precipitated  as  sulphides 
Sb2S3,  SnS  or  SnS2,  etc., 
with    sulphureted    hydrogen. 
The  first  three  are  soluble  in 
yellow  ammonium  sulphide  or 
sodium  sulphide;  the  others, 
not. 

327 


328 


MODERN  CHEMISTRY 


Group  III 


Iron 

Aluminum 

Chromium 

Cobalt 

Nickel 

Manganese 

Zinc 


Group  IV 


Group  V 


The  first  three  are  precipi- 
tated  as  hydroxides  with  am- 
monia, and  constitute  division 
one  of  this  group.  The  last 
four  are  precipitated  by  am- 
monium sulphide  as  sulphides. 

Precipitated  as  carbonates, 


Calcium 

Strontium 

Barium          j  with     ammonium     carbonate 

Magnesium  j  from  an  alkaline  solution. 


CaCO3,  SrCO3,  etc., 


Lithium 
Ammonium 
Sodium 
Potassium 


Not  precipitated  by  any  com- 
mon reagents.  Most  of  them 
usually  tested  by  color  impart- 
ed to  flame,  or  the  spectrum.  . 


The  General  Plan.  —  Suppose  now  we  have  a  solution 
which  may  contain  salts  of  any  or  all  of  the  above  metals. 
By  adding  hydrochloric  acid,  those  of  the  first  group  would 
be  precipitated  and  their  chlorides  separated  by  filtering. 
The  filtrate  would  contain  the  remaining  four  groups. 
This  would  now  be  treated  with  hydrogen  sulphide, 
whereby  the  second  group  metals  may  be  precipitated  and 
filtered  out.  In  a  similar  way  the  separation  of  the  third, 
fourth,  and  fifth  groups  would  be  effected.  All  that  re- 
mains is  to  separate  the  metals  of  each  individual  group 
and  prove  their  presence  by  means  of  some  distinctive 
test. 

Ionic  Theory.  —  A  clear  understanding  of  the  processes 
underlying  any  qualitative  analysis  is  rendered  much 
easier  by  what  is  known  as  the  Ionic  theory.  It  has  long 
been  observed  that  certain  elements  or  groups  of  elements 


APPENDIX  A  329 

always  give  the  same  distinctive  tests  with  certain  re- 
agents. For  example,  a  silver  solution  gives  the  same 
characteristic  precipitate  with  any  soluble  chloride, 
whether  it  be  hydrochloric  acid,  sodium  chloride,  or  any 
other. 

Suppose  in  analyzing  an  unknown  solution  we  have 
found  four  bases  and  four  acid  radicals :  each  base  might 
have  been  combined  with  each  of  the  acid  groups,  making 
in  all  sixteen  possible  cases.  Were  we  compelled  to  test 
for  each  one  of  these  possible  compounds,  analysis  would 
be  very  tedious ;  but,  as  already  stated,  each  base  affords 
the  same  test  as  if  it  existed  alone. 

It  seems,  therefore,  that  when  substances  are  dissolved, 
they  become  more  or  less  dissociated.  For  example, 
hydrochloric  acid  becomes  largely  broken  up  into  hydro- 
gen and  chlorine  atoms;  potassium  chlorate  into  potas- 
sium, K  and  C1O3,  groups.  As  the  solution  becomes  more 
dilute,  this  dissociation  as  a  rule  increases. 

Ions.  —  These  dissociated  atoms  or  groups  of  atoms  are 
called  ions,  and  the  process  itself,  ionization.  They  are 
regarded  as  being  charged  with  electricity,  and  are  of  two 
kinds,  anions  or  negative  ions,  and  cathions  or  positive 
ions.  The  metals,  ammonium,  and  hydrogen  are  cathions ; 
the  acid  radicals  and  elements,  like  NO3  and  Cl,  and  the 
group  HO,  hydro xyl,  are  anions.  This  is  often  called  the 
theory  of  electrolytic  dissociation,  and  concisely  stated  is 
that  when  compound  substances  are  dissolved  in  water, 
they  are  to  a  greater  or  less  extent  broken  up  into  their 
constituent  anions  and  cathions. 

Application  of  the  Theory.  —  In  the  brief  space  of  this 
text  it  is  impossible  to  make  application  of  the  theory  to 
any  extent.  For  this  the  student  is  referred  to  Ostwald's 
Analytical  Chemistry,  translated  by  McGowan.  An  illus- 


330  MODERN  CHEMISTRY 

tration  may,  however,  make  the  theory  somewhat  clearer. 
Suppose  we  have  a  solution  containing  lead  nitrate,  Pb 
(NO3)2,  silver  nitrate,  AgNO3,  and  mercurous  nitrate, 
HgNO3.  According  to  the  ionic  theory,  the  solution 
contains,  not  molecules  of  the  three  compounds  mentioned, 
but  largely  individual  ions  of  Pb,  Ag,  Hg,  and  (NO8); 
hence,  tests  need  be  made  only  for  these  four.  Now, 
when  we  add  dilute  hydrochloric  acid,  we  introduce  two 
other  ions,  H  and  Cl.  When  those  of  Pb,  Ag,  and  Hg 
meet  with  the  Cl  ions,  compounds  form,  which  in  the  main 
are  insoluble  in  water,  hence  are  not  dissociated  or  broken 
up  into  ions,  and  therefore  fall  as  precipitates.  The  same 
is  true  in  any  other  chemical  reactions. 

Details  of  the  Work.  Group  I.  —  Take  about  two-thirds 
of  the  unknown  solution,  "  Solution  A,"  and  add  to  it  a 
little  hydrochloric  acid ;  if  any  of  the  first  group  metals 
are  present,  they  will  come  down  as  a  white  precipitate. 
Filter  out  and  save  the  clear  filtrate  for  work  with  the 
remaining  groups.  We  will  label  this  "Solution  B."  To 
be  sure  that  enough  hydrochloric  acid  has  been  used,  add 
a  drop  or  two  to  this  filtrate.  If  it  becomes  turbid  more 
must  be  added,  and  the  whole  solution  again  passed 
through  the  filter  paper.  Now  wash  the  precipitate  on 
the  paper  two  or  three  times  with  cold  water,  and  throw 
out  the  wash  water.  Next  punch  a  hole  in  the  bottom 
of  the  paper,  and  by  directing  a  stream  of  water  from 
the  wash  bottle  upon  the  precipitate  wash  it  through 
into  a  beaker.  Do  not  use  too  much  water,  however  ; 
usually  50  to  75  cc.  will  be  sufficient.  If  the  precipitate 
is  not  easily  loosened  by  the  stream  of  water,  remove 
it  with  a  spatula  or  stirring  rod,  and  add  it  to  what  has 
already  been  washed  into  the  beaker.  Next,  heat  this  to. 
the  boiling  point  and  after  a  minute  or  two  filter  quickly. 


APPENDIX  A 


331 


If  any  precipitate  remains  upon  the  filter,  wash  once  or 
twice  with  hot  water. 

Tests  for  Lead  and  Mercury.  —  Lead  chloride  is  very 
soluble  in  hot  water,  and  if  it  was  present  it  will  now  be 
found  in  the  filtrate.  Test  a  portion  of  it  with  potassium 
dichromate,  K2Cr2O7 ;  another  portion,  with  potassium 
iodide,  KI,  or  sulphuric  acid.  The  first  two  give  dis- 
tinctive yellow  precipitates,  the  third,  a  heavy  white  one, 
somewhat  soluble  in  water,  but  almost  entirely  insoluble 
in  alcohol.  Any  precipitate  left  on  the  filter  paper  above 
will  contain  the  mercurous  and  silver  chlorides,  if  any 
were  present.  The  latter  of  these  is  very  soluble  in  am- 
monia ;  so  pour  upon  the  filter  paper  a  few  cubic  centi- 
meters of  ammonium  hydroxide.  If  mercury  is  present, 
the  precipitate  will  turn  black,  and  further  proof  is  un- 
necessary. 

TABLE  I 
SEPARATION  OF  LEAD,  MERCURY,  AND  SILVER 


To  the  unknown  solution, 
add  HC1,  filter  out  the  chlo- 
rides, and  wash  the  precipi- 
tates. Save  the  filtrate  for  de- 
termining metals  of  Group  II 
and  those  following.  Mark  it 
"Solution  B."  Transfer  the 
precipitates  to  a  beaker;  add 
H2O,  and  boil.  Filter,  and 
wash  with  hot  water,  if  any 
precipitate  remains.  Test 
filtrate  for  Pb  as  in  1.  De- 
termine Hg  and  Ag  in  the 
precipitate  as  in  2  and  3. 


1.  Test  the  hot  water  filtrate  for 
Pb  with  K2Cr2O7,  KI,  and  H2SO4. 
For  results,  see  preceding  work. 


2.  To  the  precipitate  left  undis- 
solved  by  the  hot  water,  add  NH4OH. 
If  it  turns  black,  mercurous  salts  are 
indicated.  Test  filtrate  that  runs 
through,  for  Ag  by  3,  below. 


3.  To  the  filtrate  from  2,  above, 
add  HNO3  till  odor  of  NH3  is  no 
longer  perceptible.  A  white  precipi- 
tate indicates  silver. 


332  MODERN  CHEMISTRY 

Test  for  Silver.  —  To  determine  whether  silver  is 
present  put  the  ammonia  solution  that  has  just  filtered 
through  into  a  test-tube  and  add  nitric  acid  until  no 
longer  alkaline.  This  will  be  known  by  the  absence  of 
the  odor  of  ammonia.  If  there  is  any  silver  present,  a 
white  precipitate  will  form,  which  may  again  be  dissolved 
by  adding  ammonia. 

Group  II. —  Through  "Solution  B,"  the  filtrate  from 
the  chlorides  of  the  first  group,  pass  a  current  of  hydro- 
gen sulphide,  until,  after  shaking  the  solution,  the  odor 
of  the  gas  is  very  perceptible.  Any  metals  of  this  group 
will  now  be  in  the  form  of  sulphides.  Warm  somewhat 
to  collect  the  precipitates,  and  filter  quickly.  Preserve 
the  filtrate,  "Solution  C,"  for  determining  metals  of  the 
third  and  succeeding  groups. 

Now  wash  the  precipitates  left  on  the  filter  and  reject 
the  wash  water.  Transfer  the  precipitates  to  an  evapo- 
rating dish  and  add  a  few  cubic  centimeters  of  yellow 
ammonium  sulphide  or  sodium  sulphide  in  solution,  and 
warm  gently  for  several  minutes.  This  will  dissolve  the 
sulphides  of  division  1  of  this  group,  that  is,  those  of 
arsenic,  tin,  and  antimony ;  while  those  in  the  second 
division,  mercuric  salts,  copper,  bismuth,  cadmium,  and, 
as  lead  chloride  is  somewhat  soluble  in  water,  sometimes 
lead,  will  remain  as  precipitates.  It  should  be  stated, 
however,  that  copper  sulphide  is  partially  soluble  in 
strong  yellow  ammonium  sulphide;  hence,  when  its  pres- 
ence is  suspected  from  the  color  of  the  original  solution, 
it  is  better  to  use  sodium  sulphide  to  separate  division 
one  from  two. 

When  the  sulphides  have  been  digested  as  stated, 
filter  and  wash  the  remaining  precipitate  with  water  to 
which  a  drop  or  two  of  ammonium  sulphide  has  been 


APPENDIX  A  333 

added.  Save  the  filtrate  to  test  for  arsenic,  tin,  and 
antimony. 

Test  for  Mercury.  —  Transfer  the  precipitates  of  mer- 
cury, copper,  etc.,  to  a  beaker,  add  a  few  cubic  centi- 
meters of  dilute  nitric  acid,  and  boil.  All  the  sulphides 
will  dissolve  except  that  of  mercury,  which  will  remain  as 
a  heavy  black  residue.  Disregard  any  dark-colored  par- 
ticles that  remain  floating  upon  the  liquid,  for  they 
consist  merely  of  sulphur  colored  with  small  portions  of 
the  black  sulphides  not  yet  dissolved.  The  student  can 
prove  this  by  collecting  them  upon  a  small  loop  in  a 
platinum  wire  and  igniting  in  the  bunsen  flame.  The 
mass  will  burn  with  characteristic  flame  and  odor.  The 
indications  of  mercury  shown  by  the  black  residue  may 
be  verified  by  filtering  out,  washing,  and  dissolving  in 
aqua  regia.  Boil  to  dry  ness,  take  up  with  water,  and  test 
one  portion  with  stannous  chloride.  A  white  precipitate, 
turning  gray  when  heated,  or  when  more  of  the  stannous 
solution  is  added,  is  distinctive.  Test  another  portion 
with  potassium  iodide,  adding  a  drop  at  a  time.  A  bright 
red  precipitate,  soluble  in  excess  of  the  reagent,  should 
form. 

The  filtrate  from  the  mercuric  sulphide,  containing 
copper,  bismuth,  etc.,  should  be  boiled  nearly  to  dryness, 
and  water  added  to  dissolve  the  salts.  Before  proceeding 
farther,  it  is  always  better,  if  lead  has  been  .found  in  the 
first  group,  to  test  a  small  portion  of  this  solution  in  water 
in  a  test-tube  with  sulphuric  acid  and  a  little  alcohol 
added.  If  a  precipitate  of  lead  sulphate  forms,  it  must 
be  removed  in  the  same  way  from  the  whole  solution, 
using  very  little  sulphuric  acid. 

Test  for  Copper.  —  Now  add  ammonia  to  the  solution, 
from  which  you  have  removed  the  lead,  until  alkaline. 


834  MODERN  CHEMISTRY 

If  the  solution  turns  darker  blue,  copper  is  indicated ; 
at  the  same  time  bismuth  will  come  down  as  a  fine  white 
precipitate.  As  the  quantity  of  bismuth  in  solution  is 
usually  small,  the  student  must  be  careful  not  to  overlook 
it ;  at  the  same  time  he  must  not  mistake  for  bismuth  a 
fine  sediment  sometimes  carelessly  allowed  to  collect  in 
the  reagent  bottle  used  for  ammonia. 

Test  for  Cadmium.  —  To  determine  whether  cadmium  is 
present,  after  filtering  out  the  bismuth,  add  to  the  blue 
solution  potassium  cyanide  in  solution,  drop  by  drop,  until 
the  blue  color  has  entirely  disappeared ;  then  pass  a 
current  of  hydrogen  sulphide,  by  which  the  cadmium,  if 
present,  will  be  precipitated  as  a  bright  yellow  sulphide. 

Tests  for  Arsenic,  Tin,  and  Antimony.  —  For  separating 
and  determining  the  presence  of  arsenic,  tin,  and  antimony, 
various  plans  have  been  suggested,  but  nearly  all  are 
more  or  less  tedious  and  require  considerable  care.  The 
following  plan,  perhaps,  is  as  satisfactory  as  any.  To  the 
ammonium  sulphide  solution  of  these  metals,  saved  above, 
add  dilute  hydrochloric  acid  till  the  solution  is  no  longer 
alkaline.  The  three  metals  will  again  be  precipitated  as 
sulphides.  If  the  precipitate  is  pale  yellow,  or  nearly 
white,  and  small  in  quantity,  it  probably  consists  mainly 
of  sulphur,  and  none  of  the  metals  need  be  sought.  If  it 
is  dark  colored,  gold  or  platinum  may  be  present,  or  if 
copper  has  been  found  in  the  other  division  of  this  group, 
and  ammonium  sulphide  was  used  instead  of  sodium  sul- 
phide, the  precipitate  may  be  only  copper.  Filter,  and 
throw  ou&  the  filtrate,  as  it  contains  no  metals.  Wash 
the  precipitate,  as  usual,  and  transfer  it  to  a  beaker. 
"/-Now  add  a  little  strong  hydrochloric  acid  and  warm 
gently ;  the  sulphides  of  antimony  and  tin  will  dissolve, 
but  the  arsenic  will  be  unaffected.  Filter,  and  test  the 


I 


APPENDTX  A  335 

filtrate  as  follows :  put  into  it  a  bright  iron  wire  or 
nail,  and  after  warming  gently  let  it  stand  about  fifteen 
minutes.  The  antimony  is  reduced  to  the  metallic  form, 
and  the  stannic  chloride  to  the  stannous.  Filter  or  de- 
cant and  test  the  solution  for  tin  with  mercuric  chloride.— (3 
The  results  are  those  given  in  testing  for  mercury 
with  stannous  chloride  in  the  other  division  of  this  same 
group. 

Wash  thoroughly  the  precipitated  antimony,  and  add 
to  it  a  little  strong  hydrochloric  acid  and  a  few  drops  of 
nitric  acid.  The  antimony  will  dissolve.  Boil  the  solution  \l 
nearly  dry  and  add  water.  A  white  precipitate  indicates 
antimony,  which  may  be  verified  by  passing  a  current  of 
hydrogen  sulphide  through  the  solution.  An  orange- 
colored  precipitate  will  result. 

The  arsenic  left  undissolved  by  the  hydrochloric  acid 
above  may  be  tested  in  several  ways.  Transfer  the  ar- 
senic sulphide  to  a  beaker,  add  to  it  some  strong  nitric 
acid,  and  heat.  The  arsenic  will  dissolve.  Now  fill  a 
test-tube  about  half  full  of  a  solution  of  ammonium 
molybdate,  add  to  it  a  few  drops  of  the  arsenic  solution 
prepared  above,  and  boil.  A  yellow  crystalline  precipi- 
tate indicates  arsenic. 

Sometimes  the  following  method  works  satisfactorily. 
After  adding  concentrated  hydrochloric  acid  to  dissolve 
the  precipitates  of  antimony— and  tin  sulphide  obtained 
from  the  ammonium  sulphide  solution,  decant  the  clear 
solution  into  a  test-tube.  Now  'slowly  pour  hydrogen 
sulphide  water  down  the  inside  of  the  tube.  Presently 
the  antimony  will  begin  to  precipitate,  forming  an  orange- 
colored  ring  of  the  sulphide.  Continue  adding  the  hy- 
drogen sulphide  solution,  when  above  the  antimony  a 
ring  of  yellow  stannic  sulphide  will  form. 


336 


MODERN  CHEMISTRY 
TABLE    FOR    GROUP   II 


<»  cc 

•*3  G 

3  *T 

o  £ 


-2?  fc 

J*   O 


CO     ^"^      _^>       fl} 

3     -j-d 

^-i     ^^        '"•'       fA 


£     ~.22 

s     3  -V 

«  2  *> 


J 


H  3  ' 

.a 


o    o 
*+"*  ,M 

O     cS 


3  .&• 

c3     O 

£   £ 


^  H 


cS     fl 

§  £» 


a.  Put  into  the  filtrate  a  bright  iron 
wire  or  nail  and  let  stand  about  15  minutes. 
A  black  scaly  precipitate  of  antimony  forms. 
Filter  out  and  test  by  b.  To  the  filtrate 
add  HgCl2,  drop  by  drop,  as  a  test  for  the 
tin. 


b.  Dissolve  the  precipitated  antimony  in 
aqua  regia,  boil  nearly  dry,  and  add  water. 
A  white  precipitate  indicates  antimony, 
verified  by  H2S,  which  gives  orange-colored 
precipitate. 


c.  Heat  the  precipitate  of  arsenic  sul- 
phide with  a  little  nitric  acid  and  add  some 
ammonium  molybdate  solution.  A  yellow 
crystalline  precipitate  will  indicate  arsenic. 


a 


PH    a  "o  ^  £    5    o  a 

.  o  £  .2  2  "  g 


a.  Deep  blue  color  indicates 
copper. 


b.  White  precipitate  indicates 
bismuth.  To  verify,  filter  out, 
dissolve  in  HC1,  boil  nearly  dry, 
and  add  H2O.  While  precipitate 
forms,  filter. 


c.  After  filtering  out  the  bis- 
muth, add  KCy  solution  till  the 
blue  color  has  disappeared.  Pass 
a  current  of  H9S.  A  yellow  pre- 
cipitate indicates  cadmium. 


Group  III.  —  Like  Group  II,  this  is  also  usually  separated 
into  two  divisions  for  convenience  in  analysis.  The  first 
includes  iron,  aluminum,  and  chromium,  precipitated  by 
ammonia  ;  the  second,  manganese,  zinc,  nickel,  and  cobalt, 
with  ammonium  sulphide  as  the  precipitant. 


APPENDIX  A  337 

To  "  Solution  C,"  the  filtrate  saved  from  Group  II,  after 
filtering  out  the  sulphides,  add  a  few  drops  of  nitric  acid 
and  boil  a  short  time.  Now  add  ammonium  chloride, 
NH4C1,  and  ammonium  hydroxide  till  alkaline.  The 
latter  reagent  precipitates  the  metals  of  the  first  division 
as  hydroxides.  Warm  the  solution,  filter  and  wash  as 
usual.  Save  the  filtrate  for  the  second  division  of  this 
group  and  the  succeeding  groups.  Transfer  the  hydrox- 
ides of  iron,  chromium,  and  aluminum  to  a  beaker,  add  20 
or  25  cc.  of  strong  potassium  hydroxide  solution,  and  boil 
several  minutes.  This  will  dissolve  the  aluminum  and 
leave  the  others  unchanged.  Filter  and  wash.  To  a  por- 
tion of  the  filtrate,  after  acidulating  with  hydrochloric 
acid,  add  ammonia  till  alkaline.  A  white,  flaky,  some- 
times starchy  precipitate  indicates  aluminum. 

Test  for  Iron.  —  Take  a  portion  of  the  iron  and  chro- 
mium precipitate  left  undissolved  and  add  hydrochloric 
acid.  Test  the  solution  obtained  for  iron,  by  using  either 
potassium  sulphocyanide,  KSCy,  or  potassium  ferro- 
cyanide. 

Test  for  Chromium.  —  Next,  take  a  rectangular  piece  of 
platinum  foil  and  bend  up  the  sides  so  as  to  form  a  small 
boat  or  pan.  A  piece  of  broken  porcelain  dish  may  serve 
the  same  purpose,  but  more  heat  will  be  needed.  Put  into 
the  boat  the  remaining  iron  and  chromium  precipitate,  add 
an  equal  amount  of  potassium  nitrate,  KNO3,  and  as  much 
sodium  carbonate,  Na2CO3,  and  heat  red  hot  until  the 
whole  mass  has  fused  well  together.  Upon  cooling,  if 
chromium  is  present,  it  will  assume  a  yellowish  appearance. 
Put  the  boat  and  contents  into  a  beaker  containing  a  little 
water  and  dissolve  the  mass.  Acidulate  the  solution  with 
acetic  acid  and  test  a  portion  with  silver  nitrate.  A  brick 
or  blood  red  precipitate  of  silver  chromate,  Ag2CrO4,  indi- 


838  MODERN  CHEMISTRY 

cates  the  presence  of  chromium.  Test  another  portion 
with  lead  acetate,  Pb(C2H3O2)2. 

Tests  f Oi  Nickel  and  Cobalt.  —  To  the  filtrate  saved  for 
the  second  division  of  this  group,  add  some  ammonium 
sulphide.  If  precipitates  of  light  color  are  obtained,  nickel 
and  cobalt  are  not  present,  as  their  sulphides  are  black. 
If  nickel  is  present,  the  filtrate  will  often  be  of  a  dark- 
brown  color,  which  is  apt  to  lead  the  student  to  think  the 
solution  is  not  filtering  well.  Disregard  this,  mark  it 
"  Solution  D,"  and  save  for  work  with  the  fourth  group. 
After  washing  the  precipitates,  transfer  them  to  a  beaker 
and  treat  with  dilute  hydrochloric  acid  ;  the  sulphides  of 
zinc  and  manganese  will  dissolve,  while  those  of  nickel  and 
cobalt  will  remain  as  a  black  residue.  Filter  and  wash. 
Test  the  black  residue  with  the  borax  bead  ;  cobalt  gives 
the  well-known  blue  in  the  oxidizing  flame,  and  nickel, 
yellow  to  brown  or  black,  according  to  the  amount  intro- 
duced into  the  ^ead.  If  both  metals  are  present,  the  cobalt 
blue  will  obscure  the  brown,  and  further  tests  are  neces- 
sary ;  for  these  the  student  is  referred  to  any  manual  on 
qualitative  analysis. 

Tests  for  Zinc  and  Manganese. — To  the  solution  sup- 
posed to  contain  zinc  and  manganese,  after  boiling  for  two 
or  three  minutes,  add  caustic  potash  till  strongly  alkaline. 
Allow  it  to  stand  for  some  time,  for  manganese  precipitates 
slowly.  If  present,  it  may  be  filtered  out  and  the  precipi- 
tate tested  with  the  borax  bead.  It  imparts  a  beautiful 
amethyst  color.  Acidulate  the  filtrate  with  acetic  acid  and 
add  ammonium  sulphide  till  alkaline.  A  white  precipitate 
indicates  zinc.  This  is  usually  verified  by  heating  on 
charcoal,  moistened  with  a  solution  of  cobaltous  nitrate. 
A  green  mass  is  obtained ;  aluminum  compounds  treated 
in  the  same  way  give  a  blue  mass. 


APPENDIX  A 
TABLE  FOR  GROUP  HI 


339 


c 

5 

l-H 

^ 

:i 

le 

- 

1  i 

a.  Test    for    Co    with    borax    bead  — 

ft 

!i 

^ 

^ 

0 

z 

~ 

blue. 

z 

> 

Z 

^ 

c  -^ 

I 

~ 
— 

< 

~ 

> 

2  | 

b.   If  Ni  is  present  with  no  cobalt,  borax 

— 

i 

0 

| 

^ 

~ 

*    c1 

bead  will  become  yellow  to  brown  in  oxi- 

•g 

s 

aT 

1^. 

'^ 

^ 

? 

-IT  * 

dizing  flame. 

pC 

tj 

i 

rzr 

^ 

O  "« 

— 

•3 

CD 

^ 

-1" 

5 

-r  J° 

c.  Add    considerable    excess    of    KOH 

ri 

1 

•s 

C 

OD 

p 

s 

and  let  stand   for  some   time.      A   slow- 

c" 

X 

— 
--^ 

s 

3 

A; 

"^ 

- 

forming  precipitate  indicates  Mn.     Filter 

- 

0) 

> 

^0 

Q 

— 

^> 

§ 

"£  i  ^ 

and  test  filtrate   by  d.     Verify  Mn  with 

g-* 

1 

X 

-»^- 

x 

'  — 

fl 

^  *»  *§ 

borax  bead.     Amethyst  color. 

tl 

£ 

_= 

gt 

J 

'E, 

| 

B 

"^ 

|  -^^ 

d.   Acidulate  filtrate  from  c  with  acetic 

42 

eB 

- 
£ 

'o 

2 

., 

^ 

T 

'f  2  "S 

acid,    add    (NH4)2S    till    just     alkaline. 

tJ 

-r 

Cu 

^ 

J 

&.5S  •§ 

Zinc   forms  white  precipitate   of  ZnS. 

§ 

it 

^5 

QQ 

— 

b 

1 

ES 

B 

c 

,i 

E. 

a.   Filtrate  may  contain  aluminum.    Acidulate 

g 

^ 

<N 

'-^ 
g 

-^ 

with  HC1,  add  NH4OH  or  (XH4)2CO3.-    A  white 

a 

9 

£ 

S 

^f 

E. 

o 

precipitate  of  aluminum  hydroxide   shows  the 

~ 

- 

-w 

n 

c 

^ 

— 

presence  of  the  metal. 

r 

~~. 
-^ 
— 

1 

^ 

c 
^ 

-r 
5 

>. 

^ 

— 

£r^ 

b.   Dissolve  a  small  portion  of  the  precipitate 

b 

— 

- 

bO 

• 

a» 

— 

| 

—  ~ 

in  HC1  and  test  for  iron  with  KSCy,  I^FeCy,., 

| 

'-Zi 

~ 
~ 

a. 

— 

O 
1 

'i 

-3 

&0 

or  NH4OH. 

| 

•—  • 

""-r 
~ 
^ 

1 

.2 

EB 

= 

< 

I 

O 

—  ; 
•f. 

$ 

— 

'S 

c 

g 

c.    Fuse  the  remainder  in  platinum  dish  with 
KNO,and  Na2CO3.     Dissolve  in  H2O,  acidulate 

o 

r- 

73 

^s 
_ 

— 

13 

i 

i^ 

5 

with  HCgHgOj.     Test  for  Cr  with  AgNO3,  also 

9 

•— 
o 

5 

^ 

c3 

45 

with  Pb(C2H362)2. 

Group  IV.  —  For  this  use  "  Solution  D  "  saved  from 
Group  III.  It  is  better  to  make  a  preliminary  test  be- 
fore proceeding  with  the  whole.  To  do  this,  add  to  a 
small  portion  of  the  solution  to  be  analyzed  a  little 
disodium  phosphate.  If  a  white  precipitate  forms,  some 
of  the  metals  at  least  are  present,  and  all  must  be  tested 


340  MODERN  CHEMISTRY 

for.  If  so,  add  to  the  whole  ammonium  chloride,  am- 
monium hydroxide,  and  ammonium  carbonate.  A  white 
precipitate  may  contain  calcium,  strontium,  and  barium  in 
the  form  of  carbonates  ;  filter  and  wash.  Save  the  filtrate 
to  test  for  magnesium  and  fifth-group  metals. 

Test  for  Barium,  Strontium,  etc.  —  Transfer  the  precipi- 
tates to  a  beaker  and  dissolve  in  acetic  acid.  Test  a  small 
portion  of  this  with  potassium  dichromate  ;  a  light  yel- 
low precipitate  indicates  barium,  which  may  be  verified  by 
the  flame  test.  If  present  remove  it  from  the  entire  solu- 
tion by  adding  the  dichromate  and  filtering.  To  the 
filtrate  add  caustic  potash  till  alkaline  and  a  little  more 
potassium  dichromate,  when  the  strontium,  if  present,  will 
be  precipitated,  as  strontium  chromate  is  insoluble  in 
alkaline  solutions.  Remove  this  by  filtering,  and  test 
the  filtrate  for  calcium  by  adding  ammonium  oxalate. 
This  gives  a  fine  white  precipitate  of  calcium  oxalate. 
It  is  customary  to  verify  the  strontium  by  the  flame 
test,  as  its  salts  impart  a  crimson  color  which  is  very 
persistent. 

There  are  other  plans  for  effecting  a  separation  of  the 
metals  of  this  group,  of  which  the  following  is  frequently 
used.  After  removing  the  barium,  to  a  small  portion  of 
the  filtrate  add  a  little  strong  solution  of  calcium  sul- 
phate. If  a  white  precipitate  forms,  strontium  is  present 
and  must  be  removed.  Add  to  the  remainder  of  the  solu- 
tion a  very  little  sulphuric  acid  ;  the  strontium  will  slowly 
precipitate.  After  a  few  minutes  filter  and  test  filtrate 
for  calcium.  To  do  this  add  sufficient  ammonia  to  neu- 
tralize any  excess  of  sulphuric  acid  present,  and  then  add 
ammonium  oxalate  solution  as  in  other  methods. 

To  a  small  portion  of  the  filtrate  saved  above,  after  pre- 
cipitating the  barium,  strontium,  and  calcium  with  am- 


APPENDIX  A 


341 


monium  carbonate,  add  a  little  disodium  phosphate ;  a 
white  precipitate  which  may  form  slowly  will  indicate 
magnesium. 

TABLE   FOR  GROUP  IV 


S  o  g 
CS  - 

hjT  2  ts 

5  8  § 


- 


§ 


1.  To  a  small  portion  of  the  solution,  add  a  little 
K.,Cr2O7  solution.  If  Ba  is  present,  indicated  by  the 
forming  of  a  light  yellow  precipitate,  treat  the  whole  of 
the  solution  in  the  same  way,  and  filter.  The  Ba  pre- 
cipitate may  be  verified  by  flame  test.  Test  the  filtrate 
by  2. 


2.  Render  the  filtrate  alkaline  by  adding  KOH,  and 
then  add  a  little  more  K2O2Or  If  strontium  is  present, 
it  will  be  precipitated  and  may  be  filtered  out.  Or,  from 
the  filtrate  from  1  above,  the  strontium  may  be  removed 
by  adding  a  little  sulphuric  acid.  Let  it  stand  a  few 
minutes  and  then  filter,  and  test  filtrate  for  Ca  by  3. 
The  precipitate  may  be  verified  by  flame  test. 


3.  When  the  barium  and  strontium  have  been  re- 
moved, if  the  filtrate  is  not  already  alkaline,  render  it 
so  by  adding  NH4OH.  Then  add  ammonium  oxalate; 
white  precipitate  is  distinctive  of  calcium.  May  be 
verified  by  flame  test,  orange-yellow. 


4.   To  a  small  portion  of  the  filtrate   saved  from 
"Solution   D,"  add  a  little   disodium  phosphate.      A 
~  ~?        white  precipitate  indicates  magnesium,  distinctive  in 
fc.  3  j  the  absence  of  other  metals  of  this  group.     Filter,  and 
**•*  rt    save  filtrate  for  Group  V,  "  Solution  E." 


Group  V.  Sodium,  Potassium,  Lithium.  —  The  salts  of 
the  metals  of  this  group  are  all  soluble  in  water,  hence  none 
of  the  reagents  used  in  the  previous  steps  of  analysis  pre- 
cipitate them.  The  flame,  especially  with  the  spectroscope, 
is  usually  all  that  is  necessary  for  their  identification. 


342  MODERN  CHEMISTRY 

As  sodium  is  so  widely  distributed,  a  slight  test  for  it  may 
nearly  always  be  obtained,  but  the  student  must  learn  to 
disregard  any  except  a  decidedly  strong  indication.  As 
already  seen,  if  sodium  is  present,  the  potassium  flame  can 
be  perceived  only  by  making  the  observation  through  a 
sheet  of  cobalt  glass.  Before  making  these  flame  tests, 
boil  the  solution,  saved  from  Group  IV,  to  dry  ness,  and 
heat  gently  until  ammonia  fumes  are  no  longer  driven  off. 
Dissolve  the  residue  in  water,  and  acidulate  with  hydro- 
chloric acid. 

Sodium  gives  bright  yellow  flame, 

Potassium  gives  violet  flame, 

Lithium  gives  bright  red  flame,  lasting  but  a 
moment. 

Potassium  may  also  be  tested  in  another  way.  To  the 
solution  used  in  making  the  flame  tests,  add  some  platinic 
chloride  in  solution  and  a  little  alcohol.  Allow  it  to  stand 
for  some  time,  stirring  occasionally  with  a  glass  rod.  A 
small  quantity  of  a  yellow  precipitate  of  potassic-platinic 
chloride,  K2PtCl6,  is  slowly  deposited.  A  large  watch 
crystal  serves  well  for  making  this  test. 

Test  for  Ammonia.  —  Ammonia  must  be  looked  for  in 
the  original  solution,  as  so  many  ammonium  compounds 
are  used  as  reagents  in  making  the  analysis.  Put  a  few 
cubic  centimeters  of  the  original  solution  into  a  beaker 
and  add  caustic  soda  or  potash  until  strongly  alkaline. 
Moisten  the  under  side  of  a  watch  crystal  with  a  drop  of 
water  and  upon  it  place  a  short  strip  of  red  litmus  paper. 
Put  the.  crystal  over  the  beaker,  and  warm  the  solution 
gently.  If  ammonia  is  present,  it  will  be  liberated  by  the 
non-volatile  alkali  added,  and  will  turn  the  litmus  paper 
blue. 


APPENDIX  A 
TABLE  FOR  GROUP  V 


343 


1  Boil  filtrate  from  Table  IV  to  dry- 
ness,  ignite  to  expel  NH4  compounds, 
dissolve  in  H2O  and  acidulate  with 
HCI.  Test  for  Na,  K,  Li,  by  flame  as 
in  1  ;  K  by  wet  method,  as  in  2  ;  NH4, 
as  in  3. 

1.  Make  test  with  platinum  wire;  Na  gives 
yellow  ;  K,  violet  when  alone  ;  Li,  red.  Use  cobalt 
glass,  if  Na  is  present,  to  distinguish  the  violet  rays. 

2.  Sometimes  K  must  be  detected  otherwise 
than  by  the  flame  test.  To  the  acidulated  solution, 
add  PtCl4;  a  yellow  precipitate,  slowly  forming, 
indicates  K. 

3.  To  a  portion  of  the  original  solution,  add 
caustic  soda  or  potash  till  alkaline,  and  warm  gently. 
Suspend  a  strip  of  red  litmus  in  the  fumes  arising. 
If  it  turns  blue,  NH4  is  indicated. 

The  five  tables  given  above  simply  show  in  condensed 
form  the  methods  already  described  ;  and  when  the  student 
has  once  seen  the  details  and  understands  them,  he  will 
find  the  tables  very  convenient  for  rapid  work.  For  a 
successful  analysis,  neatness  is  absolutely  essential,  and 
great  care  must  be  used  in  washing  the  precipitates  so  as 
to  remove  all  of  the  metals  contained  in  the  filtrate. 

Detection  of  Acids.  —  As  a  rule,  the  beginner  will  only 
meet  with  a  few  of  the  more  common  acids,  and  these  only 
will  be  noticed  here.  They  may  be  placed  in  groups, 
somewhat  as  the  metals  are,  according  as  they  are  affected 
by  certain  reagents. 

Group  I.  —  This  includes  those  which  form  a  precipitate 
with  barium  chloride.  The  only  one  with  which  the 
student  will  meet  often  is  sulphuric  acid.  As  already 
seen,  this  gives  with  barium  chloride,  barium  sulphate, 
BaSO4,  insoluble  in  all  acids. 

If  the  solution  be  neutral,  phosphoric  acid  or  the  phos- 


344  MODERN  CHEMISTRY 

phates  also  give  a  white  precipitate  with  barium  chloride  ; 
but  this  is  soluble  in  hydrochloric  acid.  After  being  thus 
dissolved,  if  the  solution  be  made  alkaline  with  ammonia, 
the  precipitate  will  again  fall. 

Sulphurous  and  thiosulphuric  acids  are  usually  put  in 
this  group.  They  may  be  easily  distinguished,  how- 
ever. To  the  solution  add  a  little  strong  hydrochloric 
acid ;  both  sulphurous  and  thiosulphuric  acid  and  their 
salts  will  give  off  fumes  of  sulphur  dioxide  which  may  be 
readily  detected.  The  latter,  however,  at  the  same  time, 
throws  down  a  milky  or  pale  yellow  precipitate  of  sulphur, 
while  the  former  remains  clear.  The  reaction  is  shown 
below  :  — 

Na2SO3  +  2  HC1  =  2  NaCl  +  H2O  +  SO2  (sulphurous), 
Na2S203  +  2  HC1  =  2  NaCl  +  H2O  +  SO2  +  S  (thiosulphuric). 

Group  II.  —  This  includes  such  as  form  no  precipitate 
with  barium  chloride,  but  do  with  silver  nitrate.  The 
most  common  are:  — 

Hydrochloric,  HC1,  curdy  white  precipitate,  very  solu- 
ble in  ammonia. 

Hydrobromic,  HBr,  pale  yellowish  white  precipitate, 
slowly  soluble  in  ammonia. 

Hydriodic,  HI,  pale  yellow  precipitate,  very  slightly 
soluble  in  ammonia. 

Methods  for  testing  each  of  these  and  its  compounds  have 
been  given  in  the  text,  and  the  student  is  referred  to  them. 
Hydrogen  sulphide,  H2S,  if  free,  is  known  by  the  odor. 
In  the  form  of  compounds,  it  may  usually  be  detected  by 
adding  some  acid  and  heating,  whereby  the  gas  is  liberated 
and  its  characteristic  odor  becomes  perceptible. 


APPENDIX  A  345 

Group  III.  —  Here  belong  those  acids  which  form  no 
precipitate  with  either  barium  chloride  or  silver  nitrate. 
The  only  common  one  is  nitric,  but  the  salts  of  nitrous 
and  chloric  acids,  HNO2  and  HC1O3,  especially  those  of  the 
latter,  have  occasional  use  in  the  laboratory.  A  plan  for 
testing  and  distinguishing  between  nitrous  and  nitric  acids 
was  given  in  the  text.  The  following  plan,  however, 
usually  works  satisfactorily,  and  by  some  is  preferred  to 
the  other.  Into  a  test-tube,  containing  the  solution  to  be 
tested,  drop  a  crystal  of  ferrous  sulphate,  and  then  pour 
down  the  sides  of  the  tube  a  few  drops  of  strong  sulphuric 
acid.  A  brown  ring  will  form  about  the  crystal  of  ferrous 
sulphate. 

The  chlorates,  for  example,  potassium  chlorate,  KC1O3, 
heated  with  sulphuric  acid,  yield  chlorine,  and  chlorine 
peroxide,  a  very  explosive  gas.  Usually,  if  sulphuric  acid 
is  added  to  a  crystal  of  the  chlorate,  a  sharp  explosion 
occurs,  throwing  the  materials  out  of  the  tube. 

Group  IV.  —  We  might  place  here  certain  organic  acids, 
which  require  special  tests  for  identification.  The  only 
common  one  is  acetic,  HC2H3O2,  though  the  student  oc- 
casionally meets  with  one  or  two  others.  Acetic  acid  and 
its  salts  are  tested  by  adding  a  solution  of  ferric  chloride 
and  boiling.  The  solution  becomes  a  deep  red  color  which 
may  be  destroyed  by  using  hydrochloric  acid  or  mercuric 
chloride. 

Oxalic  acid,  H2C2O4,  might  be  placed  here,  though  more 
properly  in  Group  I,  as  its  salts  form  a  white  precipitate 
with  barium  chloride  in  neutral  or  alkaline  solutions ; 
this  precipitate  is  soluble  in  hydrochloric  acid,  but  not 
in  acetic. 

Preliminary  Work.  —  Before  testing  any  solution  for 
acids,  the  metals  present  should  be  determined,  other- 


346  MODERN   CHEMISTRY 

wise  the  student  may  be  greatly  misled.  If  any  are 
present  which  would  interfere  with  necessary  tests,  that 
is,  if  there  are  any  which  would  form  precipitates  with 
the  reagents  necessarily  used  in  making  the  acid  tests, 
they  must  be  removed  before  proceeding  with  the  deter- 
mination. 

Again,  if  the  unknown  substance  is  in  solution,  it  would 
be  useless  to  look  for  the  acids  whose  salts  are  insoluble 
in  water.  For  example,  if  we  have  found  lead  or  barium 
present  in  a  given  solution,  obviously  it  would  be  unnec- 
essary to  look  for  sulphuric  acid.  Hence  a  knowledge 
of  the  solubility  of  salts  is  very  important,  and  the  fol- 
lowing incomplete  table  is  given,  showing  the  solubility 
of  a  few  of  the  more  common  salts:  — 

Acetates,  soluble  in  water. 

Bromides,  nearly  all  soluble ;  exceptions,  those  of  first 
group  metals  and  mercuric. 

Carbonates,  only  those  of  Group  V,  the  alkali  metals. 

Chlorides,  nearly  all,  Group  I  excepted. 

Iodides,  nearly  all,  Group  I  excepted,  also  certain 
iodides  of  bismuth  and  copper. 

Nitrates,  all  soluble. 

Nitrites,  nearly  all  soluble. 

Phosphates,  only  those  of  Group  V. 

Sulphates,  many  insoluble,  such  as  those  of  barium, 
mercury,  lead,  and  silver ;  and  calcium  and  stron- 
tium, nearly  so. 

Sulphites,  only  those  of  Group  V. 

Sulphides,  only  those  of  Groups  IV  and  V. 

If  the  substance,  of  which  the  acid  radical  is  to  be 
determined,  is  not  in  solution,  it  is  often  of  great  advan- 
tage to  make  certain  preliminary  tests.  Put  a  small  por- 


APPENDIX  A  347 

tion  of  it  into  a  test-tube  and  add  a  little  strong  sulphuric 
acid.  Warm  gently,  and  notice  the  color  and  odor  of  the 
gas  obtained.  The  more  common  are  shown  below :  — 

Acetates,  odor  of  vinegar,  no  color. 

Bromides,  sickening  odor,  brown  color,  resembling 
that  of  nitrogen  tetroxide.  Odor  is  more  offensive 
and  peculiarly  irritating  to  the  eyes. 

Carbonates,  strong  effervescence,  no  special  odor, 
colorless  gas. 

Chlorides,  very  irritating  gas  (HC1),  colorless. 

Iodides,  peculiar  odor,  resembling  weak  chlorine, 
violet  color. 

Nitrates,  very  irritating  gas,  no  color. 

Nitrites,  irritating  gas,  brown  in  color ;  not  so  offen- 
sive as  bromine. 

Phosphates,  no  special  action. 

Sulphates,  no  special  action. 

Sulphites,  saffocating  gas  (SO2),  colorless. 

Sulphides,  offensive  odor  (H2S),  colorless. 

Thiosulphates,  suffocating  gas  (SO2),  colorless. 

The  student  must  remember  that  these  are  merely  pre- 
liminary steps  and  must  be  verified  by  distinctive  tests 
already  described. 


APPENDIX  B 


SOME  ADDITIONAL  QUANTITATIVE  WORK 

IT  is  believed  that  all  the  quantitative  work  that  the 
ordinary  class  can  do  has  been  introduced  into  the  text. 
There  may  be  occasions,  however,  when  it  will  seem  desir- 
able to  vary  the  work  or  even  to  furnish  more  to  certain 
students ;  to  meet  such  a  demand,  the  following  experi- 
ments are  offered. 

1.    To  estimate  Amount  of  Carbon  Dioxide  in  any  car- 
bonate soluble  in  acids.     (Adapted  from  Fresenius.) 
Fit  two  small  bottles  with  rubber  stoppers   and  glass 

tubing,  as  shown  in  the 
figure.  E  is  a  short  piece 
of  rubber  tubing  which 
may  be  closed  air-tight  by 
means  of  a  screw  clamp. 
The  carbonate  to  be  used, 
calcite  for  example, 
CaCO3,  is  accurately 
weighed,  placed  in  M,  and 
covered  with  water.  N 
is  filled  over  half  full  of  pure  concentrated  sulphuric  acid. 
Find  the  weight  of  the  whole,  which  should  not  exceed 
60  to  70  g.,  tighten  the  clamp  at  E,  and  test  the  appa- 
ratus to  see  that  it  is  air-tight. 

Now  by  suction  at  (7,  partially  exhaust  the  air  in  JV; 
this  will  have  a  like  effect  upon  M^  and  upon  readmitting 
the  air  to  N  the  acid  will  be  forced  over  into  M.  The 

348 


FIG.  65. 


APPENDIX  B  349 

carbonate  will  thus  be  decomposed,  and  the  carbon  dioxide 
will  escape  into  JV,  being  dried  as  it  bubbles  through  the 
acid.  When  the  carbonate  has  all  been  decomposed,  and 
the  evolution  of  gas  has  ceased,  open  the  clamp  at  E,  and 
by  means  of  an  aspirator  or  by  suction  remove  the  carbon 
dioxide  from  Msmd  N,  and  when  the  apparatus  has  become 
cool,  weigh  again.  The  loss  represents  the  amount  of 
carbon  dioxide  expelled  by  the  acid. 

Carbonate  used  (for  example)       .         .       1.0  g. 
Apparatus  and  contents,  say          .         .     68.0  g. 

After  decomposition  by  acid  :  — 

Total  weight         .         .         .         .  x  g. 

Loss 68.0 -a;. 

CO2  =  68  -  x  g. 

2.  To  determine  the  Water  of  Crystallization  in  a  Com- 
pound.—  This  is  usually  done  by  heating  a  known  weight 
of  the  compound,  and  noting  the  loss.  To  illustrate,  put 
into  a  small  porcelain  crucible,  the  weight  of  which  is 
known,  about  a  gram  of  magnesium  sulphate,  and  weigh 
carefully.  Support  the  crucible  in  a  clay  triangle  upon 
an  iron  ring-stand.  With  the  Bunsen  burner  heat  cau- 
tiously at  first,  increasing  to  red  heat,  cool  slowly  and 
weigh.  Heat  a  second  time  four  or  five  minutes  and 
weigh  again.  Do  this  until  two  successive  weighings 
show  the  same  results,  then  calculate  the  per  -cent  of 
water  of  crystallization. 

Tabulate  results  thus :  — 

Weight  of  crucible  -f  MgSO4     .         .         .        a 

Weight  of  crucible  alone    .... b 

Weight  of  MgSO4     .         .         .         .  a  -  b 


350  MODERN  CHEMISTEY 

After  the  second  and  third  heating,  when  weight  was 
the  same :  — 

Crucible  +  MgSO4     .....<? 
Loss .         .         .         .         .         .         .  a  —  c 

In  the  same  way  try  some  other  salt  containing  water 
of  crystallization,  as,  for  example,  common  alum  or  copper 
sulphate. 

3.  Volumetric  Composition  of  the  Air.  —  As  the  air,  dis- 
regarding the  impurities  and  small  portions  of  other  gases 
present,  consists  of  oxygen  and  nitrogen,  we  can  remove 
the  former  by  exploding  with  hydrogen 
and  then  measure  the  residue.  For  ex- 
~>~  ample,  suppose  we  pass  into  the  eudio- 
_  air  meter  20  cc.  of  air  and  then  10  cc.  of 

hydrogen.  We  now  have  a  total  amount 
-botkgases  oj-  ^Q  cc  .  ^^  an  eiectrjc  Spark  to  ex- 
plode the  hydrogen  and  oxygen.  As 
two  parts  of  hydrogen  unite  with  one 
of  oxygen,  one-third  of  the  loss  would 
represent  the  oxygen,  and  the  other  two-thirds  the  hydro- 
gen, which  has  combined  to  form  water.  The  residue 
will  contain  the  nitrogen  of  the  air  and  any  excess  of 
hydrogen.  Take  the  quantities  used  above  :  — 

Air 20  cc. 

Air  +  H 30  cc. 

Residue  after  exploding       .         .  18  cc. 

Loss 12  cc. 

\  of  loss  =  4  cc.,  the  oxygen  of  air  used. 
20  cc.  air  =  4  cc.  oxygen  -h  16  cc.,  nitrogen 
of  air. 


APPENDIX  B  351 

Let  the  student  arrange  his  own  apparatus  for  the  above 
experiment,  making  all  corrections  necessary  for  accurate 
results,  and  prove  the  usual  statement  that  air  is  one-fifth 
o-cv^en  and  four-fifths  nitrogen. 

1  The  Volumetric  Composition  of  Ammonia.  —  The 
.{position  of  ammonia  may  be  determined,  but  the  ex- 
periment requires  time  and  is  somewhat  tedious.  The 
plan  is  as  follows:  into  a  eudiometer,  over  mercury, 
introduce  a  few  cubic  centimeters  of  dry  ammonia  gas, 
and  pass  sparks  from  an  induction  coil  for  twenty  or 
thirty  minutes  or  until  the  volume  of  the  ammonia  seems 
no  longer  to  increase.  This,  in  accordance  with  the  law 
of  Gay-Lussac,  should  now  be  double  what  was  intro- 
duced into  the  eudiometer.  Next  add  sufficient  oxygen 
to  explode  with  the  hydrogen  obtained  from  the  ammonia, 
and  pass  a  spark.  It  is  obvious,  from  the  proportions  in 
which  hydrogen  and  oxygen  combine,  that  two-thirds  of 
the  loss  represents  the  hydrogen,  which,  subtracted  from 
the  volume  of  the  gases  after  electrolysis,  gives  the 
amount  of  nitrogen  contained  in  the  ammonia.  Take  the 
following  example :  — 

Ammonia  gas  introduced         .         .         .       8  cc. 

Vol.  of  mixed  gases  after  passing  sparks,  16  cc. 

Oxygen  added 8  cc. 

Total  amount 24  cc. 

Residue  after  exploding           .         .         .  6  cc. 

Loss          .         ...         .         .         .18  cc. 

Two-thirds    of    loss  =  hydrogen,    which 

was  obtained  from  the  ammonia  gas     .  l§t;c. 

Volume   of  mixed  gases  .         .         .•       .     16  cc. 

Subtract  volume  of  H  .         .         .     12  cc. 

Volume  of  N  .4  cc. 


352  MODERN  CHEMISTRY 

This  proves  that  hydrogen  and  nitrogen  unite  in  the 
proportion  of  three  to  one  to  form  ammonia ;  furthermore 
we  have  seen  that  the  four  volumes  of  the  mixed  gases 
upon  combining  are  condensed  to  two. 

Let  the  student  arrange  his  own  apparatus,  taking 
every  precaution  to  insure  accuracy,  and,  using  different 
quantities  from  those  mentioned  above,  prove  the  truth 
of  the  preceding  statements. 

5.  Composition  by  Volume  of  Hydrochloric  Acid.  —  This 
may  be  learned  by  the  interaction  of  sodium  and  hydro- 
chloric acid,  by  which  is  formed  common  salt  and  free 
hydrogen.  In  order  to  lessen  the  rapidity  of  the  reaction, 
an  amalgam  of  sodium  should  be  used.  This  may  be 
prepared  by  putting  a  small  quantity  of  mercury  into  a 
mortar,  and  then,  by  means  of  forceps,  thrusting  small 
pieces  of  sodium,  one  at  a  time,  into  the  mercury.  Do 
this  until  a  pasty  mass  is  obtained,  which  upon  cooling 
becomes  solid.  In  preparing  the  amalgam  do  not  hold 
the  face  too  close  to  the  mortar,  as  the  combination  some- 
times takes  place  with  considerable  violence. 

The  hydrochloric  acid  gas  for  this  experiment  must  be 
dried,  either  by  bubbling  through  strong  sulphuric  acid 
or  by  passing  through  a  drying  tube  containing  bits  of 
porcelain  or  pumice  stone  moistened  with  sulphuric  acid. 
The  gas  may  be  generated  by  the  reaction  of  common 
salt  and  hydrochloric  acid  with  sulphuric  acid  as  de- 
scribed on  page  112,  Sec.  26.  If  dried  by  passing  through 
sulphuric  acid,  the  rapidity  of  evolution  of  gas  may  be 
observed  and  regulated  by  increasing  or  decreasing  the 
aniouiff  of  heat  applied. 

It  is  better,  if  possible,  to  collect  the  gas  over  mercury 
rather  than  by  downward  displacement,  for  in  this  way 
it  may  be  obtained  free  from  air. 


APPENDIX  B 


353 


For  this  experiment,  some  straight  graduated  tube 
should  be  used,  such  as  the  eudiometer  shown  in  some 
of  the  illustrations  for  the  synthesis  of  gases.  If  this 
is  not  to  be  had,  you  may  use  a  burette,  the  capacity  of 
which,  both  above  and  below  the  graduations,  is  accurately 
known.  (See  Fig.  67  for  the  general  arrangement  of  the 


FIG.  67. 

apparatus.)  When  the  graduated  tube  is  completely  filled 
with  gas,  put  around  it,  as  near  the  mouth  as  possible,  a 
paper  test-tube  holder.  This  is  made  by  folding  a  sheet 
of  paper  into  a  strip  about  an  inch  wide ;  for  use  it  is 
simply  placed  around  the  tube  as  shown  in  the  accom- 
panying figure  at  N,  and  grasped  tightly  between  the 
thumb  and  fingers.  The  paper,  being  a 
poor  conductor  of  heat,  serves  to  prevent 
the  transmission  of  the  warmth  of  the 
hand  to  the  glass  so  as  to  expand  the 
hydrochloric  acid. 

By  means  of  this  holder  seize  the  tube, 
hold  the  thumb  firmly  over  its  mouth, 
and  place  in  an  upright  position.  Next,  FIG.  68. 


354  MODERN  CHEMISTRY 

• 

quickly  drop  into  the  tube  a  few  grams  of  the  sodium 
amalgam  already  prepared,  and  instantly  replace  the 
thumb,  holding  it  as  tightly  as  possible.  Tip  the  tube 
back  and  forth  a  few  times  to  hasten  the  action,  and  when 
this  seems  complete,  place  the  mouth  of  the  tube  beneath 
the  surface  of  the  mercury  and  remove  the  thumb.  The 
mercury  instantly  rises  in  the  tube  to  fill  the  space 
formerly  occupied  by  the  chlorine,  but  now  existing  in 
the  form  of  solid  sodium  chloride.  Measure  accurately 
the  amount  of  gas  remaining,  and  compare  with  the 
capacity  of  the  tube ;  what  are  your  conclusions  ?  Test 
the  residual  gas  with  a  light ;  what  is  it  ?  What  evidence 
have  you  that  common  salt  is  formed  ? 

If  the  student  finds  he  cannot  hold  his  thumb  tightly 
enough  over  the  mouth  of  the  tube  to  prevent  leakage, 
he  may  use  a  short  rubber  stopper  instead,  and  after  the 
reaction  of  the  sodium  with  the  gas  the  tube  may  be 
opened  over  water. 

6.  Analytic  Proof  of  the  Composition  of  Hydrochloric 
Acid.  —  This  may  be  furnished  by  the  electrolysis  of 
hydrochloric  acid  and  the  measurement  of  the  gases 
obtained.  Let  the  student  arrange  his  own  apparatus, 
and,  taking  such  precautions  as  are  necessary  to  avoid 
possible  errors  (mentioned  in  describing  certain  forms 
of  electrolytic  apparatus),  make  the  experiment,  and  note 
results. 


APPENDIX  C 

SOLUTION 

1.  Meaning  of  Solution.  —  Ordinarily  we  think  of  solu- 
tion as  the  disappearance  of  a  solid  in  a  liquid,  but  in  re- 
ality the  term  is  much  broader.  Not  only  may  gases, 
solids  and  liquids  disappear  in  a  liquid,  but  one  solid  may 
dissolve  another,  or  a  solid  may  dissolve  a  liquid.  To  il- 
lustrate, Sir  Roberts-Austen  of  London,  placed  some  lead 
cylinders  upon  some  sheets  of  gold  and  allowed  them  to 
remain  for  four  years.  At  the  end  of  that  time  an  analy- 
sis showed  that  the  gold  had  penetrated  the  lead  to  the 
depth  of  8  mm.  So  other  illustrations  might  be  given. 
By  a  solution,  then,  we  mean  the  homogeneous  mixture 
of  two  or  more  substances.  The  one  in  excess  we  call  the 
solvent;  the  other,  the  solute. 

NOTE.  —  The  student  will  frequently  find  in  works  on 
volumetric  analysis  the  term  normal  solution.  By  this  we 
mean  that  in  a  liter  of  the  solution  there  is  of  the  solute 
the  equivalent  of  one  gram  of  hydrogen  ;  that  is,  of  hy- 
drochloric acid,  HC1.  there  would  be  36.5  g.  (its  molecu- 
lar weight  in  grams);  of  sodium  hydroxide,  40  g.,  and  so 
on;  of  sulphuric  acid,  H2SO4,  one  half  its  molecular 
weight,  or  49,  because  sulphuric  acid  contains  two  atoms 
of  hydrogen  ;  of  oxalic  acid,  H2C2O4,  2  H2O,  one  half  of  its 
molecular  weight  in  grams,  or  63.  A  solution  containing 
1/10  as  much  of  the  solute  as  given  above  is  called  deci- 
normal  and  marked  N/10.  The  solutions  suggested  for 

355 


356  MODERN    CHEMISTRY 

use  in  the  experiments  on  pages  168  and  169  are  deci- 
normal. 

2.  Characteristics  of  a  Solution.  —  As  solutions  of  solids 
in  liquids  are  by  far  the  most  common,  unless  otherwise 
stated  we  shall  understand  that  such  are  meant.     One  of 
the  most  notable  facts  is  that  a  solvent  has  its  boiling  point 
raised  whenever  any  substance  is  dissolved  in  it.     This 
matter  will  be  taken  up  at  more  length  later  in  this  chap- 
ter.    Another  characteristic  is  that  the  freezing  (solidify- 
ing) point  is  lowered.     Thus  it  is  well  known  that  pure 
water,  which  freezes  at  zero,  if  saturated  with  common 
salt,  requires  a  temperature  many  degrees  lower.     Another 
interesting  example  is  that  of  the  fusible  metals ;  for  ex- 
ample, "Woods'  alloy."     It  consists  of  lead,  bismuth,  tin, 
cadmium,  with  melting  points  ranging  from  335°  to  235°  C. 
and  fuses  at  65°,  much  below  the  boiling  point  of  water. 
Here  lead,  which  constitutes  the  greater  part  of  the  alloy, 
may  be  regarded  as  the  solvent,  with  a  melting  point  of  335°, 
which  by  the  presence  of  the  others  is  reduced  to  56°.    As 
there  is  always  a  contraction  of  volume  when  one  substance 
is  dissolved  in  another,  there  is  necessarily  an  increase  in 
the  specific  gravity  of  the  solution. 

3.  Theory  of  Solution.  —  In  every  substance  there  exist 
two  opposing  molecular  forces,   the    one  attractive,    the 
other  repellent.      When  a  solid  is  brought  into  contact 
with  a  liquid,  the  adhesion  of  the  liquid  and  solid  mole- 
cules acts  in  conjunction  with  the  repellent  force  among 
the   molecules   of    the    solid,    weakening   it    to   such   an 
extent  that  the  particles  of  the  solid  pass  into  the  liquid. 
This  continues  until  as  many  molecules  of  the  solid  return 
to  it  in  a  given  time  as  are  given  off,  when  equilibrium 
obtains,  and  the  solution  is  said  to  be  saturated. 

In  dilute  solutions  we  have  conditions  of  the  solute  sim- 


.   APPENDIX    C  357 

ilar  to  that  of  a  gas.  That  is,  the  molecules  of  the  dissolved 
substance  are  separated  to  such  an  extent  that,  as  Van't 
Hoff,  the  great  Dutch  chemist,  has  shown,  they  practically 
obey  all  the  laws  of  gases.  It  is  thus  that  we  are  able  to 
explain  the  osmotic  pressure  of  liquids. 

4.  Influence  of  Heat  upon  Solution.  —  As  a  rule  the  solu- 
bility of  solids  is  increased  when  the  temperature  is  raised, 
In  some  cases  the  increase  is  very  marked.     The  table 
below  shows  the  solubility  of  a  number  of  substances  in 
100  cc.  of  water  at  different  temperatures  :  — 

0°  C.  100°  C. 

Potassium  alum 3.9  357.48 

Silver  nitrate 120.0          1000.00 

Common  salt 35.60  39.80 

5.  Solution  of  Gases.  —  Gases  when  brought  into  con- 
tact with  a  solvent  may  disappear  in  it,  forming  a  true 
solution,  or  they  may  unite  with  the  liquid,  forming  what 
we  call  a  chemical  solution.      In  both  cases  a  rise  of  tem- 
perature decreases  the  solubility  of  the  gas.     Like  solu- 
tions of  solids,  this  effect  of  temperature  is  very  different. 
Notice  the  solubility  of  the  several  gases  in  1  cc.  of  water 
at  the  different  degrees:  — 

0°  C.  50°  C.  100°  C. 

CO2  .  .  .        1.78  cc.  0.5  cc.                        Occ. 

H2S  .  .  .         4.37  2.00                             0 

NH3  .  .  .  1148.00  306.00                             0 

HC1  .  .  .     503.00  364.00  12 

6.  Effect  of  Pressure.  —  According  to  the  kinetic  theory 
of  gases  their  pressure  is  due  to  the  bombardment,  so  to 
speak,  of  the  molecules  upon  the  containing  surface.     It 
follows,  therefore,  that  if  the  pressure  upon  a  gas  in  con- 
tact with  a  liquid  be  doubled,  twice  as  many  impacts  of 
the  gaseous  molecules  with  the  liquid  must  result.    Hence, 
other  conditions  being  the  same,  twice  as  much  of  the  gas 


358  MODERN    CHEMISTRY 

must  be  dissolved  in  the  liquid.  This  has  been  expressed 
in  what  is  known  as  Henry's  Law,  which  may  be  stated 
thus  :  The  amount  of  gas  dissolved  by  a  certain  volume  of 
any  liquid  is  proportional  to  the  pressure. 

Ordinary  soda  water  is  a  familiar  instance  of  the  solution 
of  a  large  quantity  of  gas,  owing  to  high  pressure.  In 
this  case,  as  soon  as  the  water  is  allowed  to  flow  into  the 
open  glass,  where  only  the  pressure  of  the  air  is  upon  it, 
the  gas  begins  to  escape  rapidly.  To  illustrate  further, 
100  cc.  of  water  at  zero  and  one  atmosphere  pressure  will 
dissolve  180  cc.  of  carbon  dioxide,  while  at  4  atmospheres, 
720  cc.  When  we  think  of  the  great  pressure  upon  sub- 
terranean streams  of  water  and  remember  that  limestone 
is  soluble  in  water  charged  with  carbon  dioxide,  the  for- 
mation of  vast  caves  seems  very  reasonable. 

7.  Conductivity  of  Substances.  —  In  studying  electroly- 
sis of  water,  it  will  be  remembered  that  a  little  sulphuric 
acid  was  added  to  the  water  in  order,  as  was  said,  to 
increase  the  conductivity.     If  an  attempt  be  made  to  pass  a 
current  of  electricity  through  pure  water,  it  will  be  found 
that  water  is  a  non-conductor.     Further,  it  will  be  found 
that  pure  sulphuric  acid  or  liquid  hydrochloric  acid  will 
not  conduct  the  current.     Again,  if  the  terminals  of  a 
battery  be  brought  into  contact  with  a  lump  of  salt  or 
any  similar  compound,  no  current  is  transmitted.     Never- 
theless, if  either  of  the  acids  mentioned,  or  the  salt,  be 
added  to  the  pure  water,  which  it  will  be  remembered  is  a 
non-conductor,  the  solution  becomes  a   good  conductor. 
These  phenomena  indicate  that  some  important  change 
has  taken  place  in  one  or  both  of  the  substances. 

8.  Other  Phenomena.  —  It  has  already  been  stated  that 
any  solvent  has  its  boiling  point  raised  when  a  substance 
is  dissolved  in  it.      For  example,  water  saturated  with 


APPENDIX   C  359 

common  salt  boils  at  108°  C.;  saturated  with  potassium 
nitrate,  116°;  with  calcium  chloride,  179°.  Numerous  exper- 
iments have  shown  that  this  elevation  of  the  boiling  point 
is  proportional  to  the  quantity  of  the  substance  dissolved; 
furthermore,  it  has  been  found  that  to  secure  a  like  change 
in  the  lowering  of  the  vapor  tension,  with  different  sub- 
stances, amounts  proportional  to  their  molecular  weights 
must  be  used.  (See  page  68.)  To  illustrate,  suppose  the 
molecular  weight  of  the  compound  A  is  342  and  of  B  46; 
then  to  secure  like  results  in  lowering  of  vapor  tension, we 
should  be  required  to  dissolve  portions  of  the  compounds 
in  the  ratio  of  342  to  46.  Such  substances  are  sometimes 
said  to  give  a  normal  rise  in  boiling  point. 

9.  Exceptions.  —  A    large   number  of   substances,  like 
common  salt,  cause  a  lowering  of  the  vapor  tension  about 
double  what  we  should  expect  from  the  above  statement. 
Many  others,  like  calcium  chloride,  cause  a  lowering  three 
times,  etc. 

10.  Freezing   Points.  —  Such  substances  as  show  what 
we  have  spoken  of  as  a  normal  lowering  of  vapor  tension 
likewise  lower  the  freezing  points  of  their  solvents  in  the 
same   way.      For   example,    if   a   gram-molecule    (grams 
equal  to  the  molecular  weight  of  the  compound)  of  cane 
sugar,  342  g.,  be  dissolved  in  a  liter  of  water,  the  solution 
freezes  at  —1.8°  C.     Likewise  a  gram-molecule  of  grape 
sugar,  180  g.,  dissolved  in  a  liter  of  water,  lowers  the 
freezing  point  to  —1.8.°     And   so   all  those   substances 
which  raise  the  boiling  point  normally,  lower  the  freezing 
point   approximately   as   given.      But   if   we   dissolve    a 
gram -molecule    of   common  salt  in  a  liter  of   water,  the 
freezing  point  is  lowered  about  3.5°,  which  is  practically 
twice  that  of  the  others  given.     What  is  true  of  this  is 
also  true  of  all  other  similar  compounds. 


360  MODERN    CHEMISTRY 

11.  Osmotic  Pressure.  —  The  same  variations  are  found 
in  osmotic  pressure.     Such  substances  as  lower  the  freezing 
point  normally  exert  an  osmotic  pressure  proportional  to 
their  molecular  weights,  but  substances  belonging  to  what 
we  have  noted  as  exceptions,  show  an  increase  in  pressure 
as  in  other  respects  named. 

12.  Some  Related  Facts. — A  further  study  of  the  sub- 
stances shows  that  those  which  cause  a  normal  lowering  of 
vapor  pressure,  etc.,  in  solution  are  non-conductors,  while 
the  others  render  the  solutions  good  conductors.     Thus, 
cane  sugar,  belonging  to  the  normal  class,  shows  a  con- 
ductivity exceedingly  small.     Acids,  bases,  and  salts  (see 
Chapter  X)  in  solution  are  excellent  conductors. 

13.  Dissociation  by  Heat. — At  a  temperature  of  about 
2500°  C.  steam  is  about  half  decomposed  into  oxygen  and 
hydrogen  molecules.     It  is  impossible,  however,  to  decom- 
pose all  of  the  molecules,  no  matter  how  long  the  heat  is 
applied,  for  there  are  as  many  molecules  of  water  formed 
by   the  recombination  of   its    components   as   are   being 
broken  up  by  the   heat.     Such   decomposition  as  this  is 
spoken  of  as  dissociation.     Iodine  above  600°  C.   has   a 
density  only  half  what  it  has  below  600°;   this  indicates 
that  the  molecules  of  iodine  have  become  dissociated  by 
the  heat.     (See  Chapter  XVI.)     The  same  has  been  found 
to  be  true  of  sulphur.     (See  section  7,  page  175.)    It  must 
be  borne  in  mind  that  dissociation  is  not  decomposition 
such  as  we  have  when  mercuric  oxide  is  heated  strongly. 
In  that  case  the  mercuric  oxide  molecules  are  not  reformed, 
while  in  dissociation,  when  the  producing  cause  is  removed, 
the  molecules  go  back  to  their  former  conditions.     Thus, 
H20  ;£  H2  +  O,  NH4C1  ^±  NH3  +  HC1,  I4  ^  2  I2. 

14.  Dissociation   by   Solution.  —  As  various  substances 
are  dissociated  by  heat,  so  others  are  when  taken  up  by 


APPENDIX    C  361 

water  or  other  solvents.  This  fact  has  been  learned  by 
determining  their  molecular  weights  in  solution.  Without 
showing  how  the  formula  was  derived,  the  following  has 
been  found  to  be  true  :  — 


in  which  Mis  the  molecular  weight  of  the  dissolved  sub- 
stance ;  K,  a  constant  factor  ;  j9,  the  concentration  of  the 
solution,  that  is,  the  amount  of  the  solute  per  1-00  g.  ; 
d,  the  lowering  of  the  freezing  point  (or  vapor  tension). 
By  using  dilute  solutions  and  determining  the  lowering  of 
the  freezing  point,  or  of  the  vapor  tension,  and  substitut- 
ing in  this  formula,  we  are  able  to  determine  the  molecular 
weight  of  the  substance  dissolved.  As  long  as  we  are 
dealing  with  what  we  have  spoken  of  as  normal  substances, 
the  results  are  very  nearly  in  accord  with  results  de- 
termined by  other  methods.  But  when  we  come  to  deal 
with  the  abnormal  substances,  we  obtain  results  one  half, 
one  third,  etc.,  what  they  should  be  theoretically.  It  must 
be  concluded,  therefore,  that  the  molecules  have  been 
dissociated  by  the  solvent  as  they  were  in  other  cases 
by  heat.  Such  dissociation  by  a  liquid  we  call  ionization, 
and  the  dissociated  parts  are  known  as  ions. 

15.  Relation  to  Conductivity.  —  From  the  fact  that  only 
solutions  which  show  the  irregularities  above  mentioned 
are  conductors,  as  well  as  for  some  other  reasons,  it  is 
concluded  that  electric  conductivity  is  by  means  of  ions. 
Such  substances  as  are  thus  dissociated  are  called  electro- 
lytes, and  the  decomposition  is  spoken  of  as    electrolytic 
dissociation. 

16.  Positive  and  Negative  Ions.  —  Whenever  any  com- 
pound is  dissociated,  two  kinds  of  ions  are  formed,  positive 
and  negative.     For  example,  common  salt  gives  positive 


362  MODERN    CHEMISTRY 

+ 
sodium   ions,  Na,  and  negative  chlorine  ions,  Cl.     This 

may  be  readily  shown  by  a  simple  experiment.  If  a  V- 
shaped  tube  be  partly  filled  with  a  dilute  solution  of  com- 
mon salt  and  a  current  of  electricity  be  passed  through  it, 
the  sodium  ions  will  move  toward  the  negative  electrode 
and  the  chlorine  toward  the  other.  This  may  be  seen  by 
using  a  few  drops  of  phenol-phthalein  in  the  salt  solution 
or  sufficient  blue  litmus  solution  to  color  it.  From  the 
law  of  electrical  attraction  and  repulsion,  therefore,  we 
know  that  the  sodium  ions  are  positive  and  the  chlorine 
negative. 

17.  Ions  not  Atoms.  —  It  is  important  to  know  that  ions 
are  not  atoms,  but  electrically  charged  atoms  or  groups  of 
atoms.     Thus  we  may  have  either  simple  or  complex  ions: 
common  salt  dissociates  necessarily  into  sodium  and  chlo- 
rine, simple  ions  positively  and  negatively  charged.     Sal 

ammoniac,  ammonium  chloride,  breaks  up  into  ammonium, 

+ 

NH4,  a  complex  positive  ion,  and  chlorine,  a  simple  nega- 
tive ion.  Again,  potassium  chlorate  dissociates  into  potas- 
sium, simple  positive,  and  chlorate,  C1O3,  complex  negative, 
ions. 

18.  Application    to    Electrolysis.  —  According   to   this 
theory,  electrolysis  is  not  due  to  the  breaking  up  of  the 
water  molecules  by  the  electric  current;  but  the  ions  pres- 
ent simply  serve  as  carriers  for  the  current  and  give  up 
their  charges  to  the  electrodes.     For  example,  when  com- 
mon salt  is  put  into  water,  it  is  broken  up  into  the  ions 
sodium  and  chlorine.     When  the  current  is  turned  on,  the 
sodium  cathions  are  repelled  from  the  anode,  and  move 
across  to  the  cathode,  where  they  become  discharged  from 
contact  with  the  cathode.     But  sodium  atoms  in  the  pres- 
ence of  water,  as  the  student  knows,  at  once  decompose 


APPENDIX    C  363 

the  water  molecules,  forming  sodium  hydroxide  and  free 
hydrogen.  This  gas  soon  begins  to  collect  in  bubbles  upon 
the  cathode  and  shortly  after  to  rise  through  the  water. 
The  chlorine  ions  are  attracted  to  the  anode,  and  in  their 
turn  give  up  their  negative  charge  to  the  positive  electrode, 
becoming  free  chlorine  atoms.  But  chlorine  in  water  at 
once  begins  to  decompose  it  (see  section  18,  page  109), 
forming  hydrochloric  acid  and  setting  free  oxygen. 
Thus  bubbles  of  oxygen  soon  begin  to  rise  from  the  anode. 
The  hydrochloric  acid  formed  at  the  anode  is  then  again 
dissociated  and  the  process  continues  indefinitely. 

19.  Ions  present  in  a  Solution.  —  When  one  tenth  of  a 
gram-molecule  of  potassium  chloride  is  dissolved  in  a  liter 
of  water,  about  75  per  cent  of  the  molecules  are  dissoci- 
ated.    We  might  represent  it  thus:  — 

100  KC1  ±£  75  K  +  75  Cl  +  25  KC1. 

This  means  that  some  of  the  ions  are  constantly  uniting 
to  form  molecular  potassium  chloride,  while  other  like  ions 

are  being  formed.     But  water  is  very  slightly  ionized  and 

+  + 

gives  H  and  HO  ions.     Now  whenever  a  H  ion  meets  a 

Cl  ion,  a  molecule  of  hydrochloric  acid  forms,  until  a  cer- 

+ 
tain  equilibrium  is  reached.     In  the  same  way  the  K  and 

HO  ions  form  molecular  potassium  hydroxide.     Hence  in 

+    + 
such  a  solution  we  should  have  not  only  the  ions,  K,  H, 

Cl,  HO,  but  also  the  molecules  KC1,  H2O,  NaHO,  and 
HC1. 

20.  Chemical   Action  Ionic.  —  From  a  large  number  of 
experiments  which   cannot  be  given  here,  and  for  other 
reasons,  it  is  believed  that  chemical  action  always  takes 
place  between  ions.     For  example,  granulated  zinc  in  dry 


3G4  MODERN    CHEMISTRY 

liquid  hydrochloric  acid  shows  no  chemical  action  what- 
ever; so  silver  nitrate  added  to  hydrochloric  acid  dissolved 
in  benzene  in  which  the  acid  is  not  ionized,  gives  no  trace 
of  the  familiar  white  precipitate.  When  we  neutralize 
a  solution  of  caustic  potash  with  hydrochloric  acid  (see 
Chapter  X),  at  first  we  have  the  four  kinds  of  ions  and  the 
four  of  molecules  already  named.  As  all  strong  acids  and 
bases  as  well  as  salts  ionize  to  about  the  same  extent,  we 
soon  have  an  equilibrium  of  all  these  eight  substances,  which 
holds  until  we  begin  to  boil  the  solution  down.  As  evap- 
oration proceeds,  the  solution  becomes  saturated,  and  crys- 
tals of  the  chloride  begin  to  separate  from  the  solution. 
As  these  deposit,  the  equilibrium  is  destroyed  and  more  of 
the  molecular  acid  and  alkali  ionize  and  more  molecular 
potassium  chloride  forms.  This  in  turn  crystallizes,  and 
so  the  process  continues  until  all  the  molecules  of  hydro- 
chloric acid  and  of  potassium  hydroxide  have  ionized,  so 
that  when  the  water  has  been  entirely  evaporated,  only 
molecules  of  potassium  chloride  remain. 


APPENDIX  D 

SOME  CARBON  COMPOUNDS 

\\TE  have  already  studied  a  few  carbon  compounds. 
The  three  hydrocarbons,  methane,  ethylene,  and  acetylene, 
may  serve  as  the  starting  point  for  a  very  large  number  of 
similar  compounds.  This  will  be  seen  from  the  following : 

CH4       .      Methane  C2H4     .    Ethylene 

C2H6      .      Ethane  C3H6      .     Propylene 

C3H8      .      Propane  C4H8      .     Butylene 

C4H10     .      Butane  C5H10    •     Ainylene 

CnH2n  +  2       General  formula       CnH2w    .     General  formula 

C2H2    .  .     Acetylene 

C3H4    .  .     Allylene 

CnH2n_2  General  formula  for  the  series 

In  all  three  series  it  will  be  noticed  that  the  difference  in 
the  formulae  of  any  two  consecutive  compounds  is  always 
CH2. 

Derivative  Compounds.  —  If  methane  be  treated  with 
chlorine,  the  hydrogen  may  be  partly  or  wholly  removed, 
giving  a  series  of  chlorine  compounds  with  hydrogen. 
Thus:  — 

CH4  +  C12  -^  CH3C1  +  HC1. 

By  further  treatment  we  may  remove  the  other  hydrogen 
atoms,  forming  successively  CH2C12,  CHC13,  CC14.  We 
call  such  compounds  derivatives  or  substitution  products.  It 
will  be  readily  seen  that  by  using  a  variety  of  substances, 

^365 


366  MODERN    CHEMISTRY 

a  vast  number  of  substitution  products  might  be  obtained. 
For  example,  we  might  substitute  bromine  or  iodine,  or  a 
large  number  of  other  substances,  for  the  hydrogen,  as  we 
have  chlorine. 

Chloroform  and  lodoform.  —  Two  of  the  simpler  deriva- 
tives from  methane  are  chloroform,  CHC13,  and  iodoform, 
CHI3,  both  of  which  are  extensively  used  in  medicine, 
the  first  as  an  anaesthetic,  the  second  as  a  deodorant  or 
germicide. 

Preparation.  —  Chloroform  is  prepared  by  treating 
alcohol  with  bleaching  powder  and  distilling.  lodoform 
is  obtained  when  a  solution  of  sodium  carbonate  in  water 
and  alcohol  is  heated  to  60°  or  75°  C.,  and  iodine  care- 
fully added.  Yellow  crystals  of  iodoform  are  slowly 
deposited. 

Characteristics.  —  Chloroform  is  a  colorless  liquid,  with 
a  specific  gravity  of  1.526,  boiling  point  62°  C.,  pleasant 
ethereal  odor,  and  produces  anaesthesia  when  inhaled  for 
some  time.  lodoform  is  a  light-yellow  solid,  melting  point 
119°  C.,  peculiar  disagreeable  odor,  and  strong  germicide. 

Other  Substitution  Products. — If,  instead  of  substituting 
an  element,  such  as  chlorine  or  iodine  for  hydrogen,  in 
such  compounds  as  methane,  we  introduce  a  group  of 
elements,  as  hydroxyl,  we  obtain  another  well-known 
series.  Thus  :  — 

CH4  gives  CH3HO,  Methyl  alcohol 

C2H6  "      C2H5HO,  Ethyl  alcohol 

C3H8  "      C3H7HO,  Propyl  alcohol 

C4H10          "     C4H9HO,  Butyl  alcohol 

CsHi2          "      C5HnHO,  Amyl  alcohol 

0,11*+,      "      CnH2ra  +  1HO,  General  formula  for  alcohols 

It  will  be  seen  that  the  alcohols  of  this  series  differ  in 


APPENDIX    D  367 

their  formula  by  CH2,  as  was  the  case  with  the  hydro- 
carbons named  above. 

Ethyl  Alcohol.  —  This  is  the  best  known  of  the  alcohol 
series,  and  is  often  called  grain  alcohol  or  spirit  of  wine. 

Fermentation.  —  The  commercial  supply  of  alcohol  comes 
from  the  fermentation  of  that  variety  of  sugar  known  as 
glucose  or  grape  sugar.  The  chemical  change  may  be 
represented  thus  :  — 


Ordinary  or  cane  sugar  will  not  ferment  unless  first  in- 
verted into  grape  sugar.  The  process  of  fermentation  is 
caused  by  germs  found  in  the  air  in  abundance.  As  these 
germs  differ,  so  we  have  different  kinds  of  fermentation. 

One  of  the  most  familiar  is  that  of  lactic  acid  fer- 
mentation, in  which  milk  sugar  is  changed  into  lactic  acid. 
Another  species  of  ferments,  as  these  germs  are  called,  has 
the  power  of  breaking  up  very  dilute  solutions  of  alcohol 
and  changing  it  into  vinegar  or  acetic  acid.  It  is  thus 
that  the  farmer  makes  his  cider  vinegar. 

A  third  variety  is  that  found  in  yeast,  and  is  known  as 
vinous  ferment.  It  has  the  power  of  converting  sugar  into 
alcohol,  with  carbon  dioxide  set  free.  This  has  been 
shown  above  in  the  equation. 

Distillation.  —  The  alcohol  obtained  by  the  inversion 
of  the  starch  in  grain  to  grape  sugar  and  subsequently 
fermenting  it,  is  not  only  impure,  but  contains  a  large 
amount  of  water.  By  repeated  fractional  distillation 
and  filtering  through  charcoal  a  product  about  96  per  cent 
alcohol  is  obtained.  To  remove  this  remaining  4  per  cent 
of  water  and  obtain  absolute  alcohol  is  somewhat  difficult, 
and  such  dehydrating  agents  as  lime  and  anhydrous 
copper  sulphate  are  used. 


368  MODERN    CHEMISTRY 

Characteristics  of  Alcohol.  —  Ethyl  alcohol  is  a  colorless 
liquid  of  pleasant  odor.  It  has  a  boiling  point  of  78.3°  C., 
and  is  readily  solidified  by  liquid  air.  Like  paraffine  and 
the  various  resins,  its  melting  point  is  rather  indefinite. 
Upon  being  removed  from  a  liquid  air  bath  it  is  first 
brittle,  but  gradually  softens,  becomes  pasty,  and  finally 
melts.  It  is  an  excellent  solvent,  and  is  thus  used  in 
preparing  various  tinctures  for  medicines,  perfumes,  ex- 
tracts, varnishes,  etc.  It  burns  with  a  slightly  luminous 
flame,  and  is  thus  used  often  for  heating  purposes. 

Methyl  Alcohol.  — This  is  also  known  as  uwood  spirit." 
It  is  obtained  in  impure  form  when  wood  is  distilled  in 
the  preparation  of  charcoal. 

Characteristics.  —  Wood  alcohol  is  a  colorless  liquid 
with  a  -rather  unpleasant  odor.  Its  boiling  point  is 
66.7°  C.  It  is  even  more  poisonous  than  ethyl  alcohol,  is 
an  excellent  solvent  for  resins  and  similar  substances,  and 
being  cheaper  than  ordinary  alcohol  is  commonly  used 
for  such  purposes. 

Organic  Acids.  —  A  series  of  acids  corresponding  to  the 
alcohols  is  known,  the  two  most  common  of  which  are 
formic  and  acetic  acid.  The  relation  is  shown  below. 

ALCOHOLS  ACIDS 

CH3OH      .     .     Methyl  CH2O2  .     .     Formic 

C2H5OH     .     .     Ethyl  C2H4O2  .     .     Acetic 

C3H7OH     .     .     Propyl  C3H6O2  .     .     Propionic 

C4H9OH     .     .     Butyl  C4H8O2  .     .     Butyric 

By  examining  the  formulae  of  the  acid  series,  it  will  be 
seen  that  each  one  has  two  less  atoms  of  hydrogen  than 
the  corresponding  alcohol,  and  one  more  of  oxygen. 
Theoretically,  the  acid  in  each  case  may  be  formed  by  the 
oxidation  of  the  alcohol,  thus  :  — 

C2H5HO  +  02  ->  H20  +  C2H402. 


APPENDIX    D  369 

Formic  Acid.  —  In  nature  formic  acid  is  found  in  the 
bodies  of  red  ants,  from  which  it  receives  its  name,  and 
in  some  nettles.  It  is  a  colorless  liquid,  which  blisters 
the  skin,  when  pure,  causing  intense  pain. 

Acetic  Acid. — Dilute  acetic  acid,  more  or  less  impure, 
is  known  to  every  one  in  the  form  of  vinegar.  To  a 
limited  extent  it  is  often  prepared  by  allowing  the  juice  of 
apples  or  other  fruit  to  ferment.  The  germ  which  brings 
about  this  decomposition  is  popularly  known  as  "mother  of 
vinegar,"  and  technically,  as  Mycoderma  aceti.  Poor  wine  is 
often  made  into  vinegar  by  allowing  it  to  remain  exposed  to 
the  air  for  a  considerable  time.  If,  however,  the  wine  is 
allowed  to  pass  slowly  through  tanks  filled  with  shavings 
which  have  been  treated  with  mother  of  vinegar,  the  process 
of  oxidation  is  very  rapid.  Commercial  acetic  acid  is  often 
obtained  as  one  of  the  products  of  distilling  wood.  The 
impure  acid  thus  formed  is  converted  into  sodium  acetate 
by  treating  the  distillate  from  the  wood  with  sodium  car- 
bonate; then  sulphuric  acid  is  added,  and  the  mixture 
distilled,  when  acetic  acid  comes  over. 

Characteristics.  —  Pure  acetic  acid  is  a  colorless  liquid 
with  a  boiling  point  of  119°  C.,  melting  point  16.7°  C. 
Such  acid  is  known  as  glacial  acetic.  It  has  a  sharp,  pene- 
trating odor  and  readily  takes  up  moisture  from  the  air. 

Aldehydes.  —  We  have  seen  above  the  relation  between 
the  alcohols  and  acids.  If  the  oxidation  is  not  allowed  to 
go  so  far,  we  may  obtain  products  between  the  alcohols 
and  acids.  Thus  :  - 

ALCOHOLS  ALDEHYDES  ACIDS 

CHoOH  CH2O  CH2O2 

C,H5OH  C9H40  C2H462 

C,H7OH  C3H60  C,H602 

CH3OH  +  O  -^  CH2O  +  H2O 
CH3OH  +  O2  ->  CH2O2  +  H2O 


370  MODERN    CHEMISTRY 

It  will  be  seen  that  the  aldehydes  are  alcohols  with 
two  atoms  of  hydrogen  removed,  while  the  acids  are 
aldehydes  with  an  additional  atom  of  oxygen. 

Formic  Aldehyde,  Methyl  Aldehyde,  CH20.  —  Formic 
aldehyde  is  prepared  by  passing  the  vapor  of  methyl 
alcohol  mixed  with  air  over  a  red-hot  copper  gauze  or 
platinum  spiral.  The  hot  metal  seems  to  serve  as  a 
catalytic  agent.  Formic  aldehyde  is  a  gas,  with  a  boiling 
point  of  —21°  C.  The  commercial  solution  contains 
about  40  per  cent  of  the  gas.  It  has  a  very  irritating 
odor,  and  is  used  largely  as  a  preservative. 

Ethers.  —  Their  relation  to  the  marsh  gas  series  may 
be  seen  from  the  following:  — 

CH4      .     .     Methane  (CH3)2O      .     .     Methyl  ether 

C2H6    .     .     Ethane  (C2H5)2O    .     .'     Ethyl  ether 

The  second  of  these  is  the  one  familiar  to  students  of 
chemistry  and  is  often  called  "sulphuric  ether."  It  was 
given  this  name  from  the  fact  that  sulphuric  acid  is 
used  in  its  manufacture.  The  process  consists  in  the 
careful  distillation  of  a  mixture  of  alcohol  and  sulphuric 
acid.  The  ether  distills  over  and  is  condensed.  There 
are  two  reactions  :  - 


C2H5OH  +  H2S04  ->     ]_j5       S04  +  H20. 

This  corresponds  to  the  formation  of  an  acid  salt  when 
sulphuric   acid   is   treated  with  caustic   soda   or   potash, 

thus  :  — 

NaHO  +  H2SO4  ->  NaHSO4  +  H2O. 

The  compound  C2H5HSO4  is  sometimes  called  the  ethyl 
ester  of  sulphuric  acid.     Next,  — 

c2H5OH  +cff  5  y  so4  ->  ^HS  \  o  +  H2so4. 


APPENDIX    D  371 

It  will  be  seen,  therefore,  that  the  sulphuric  acid  is 
regenerated  in  the  second  reaction,  and  only  additional 
amounts  of  alcohol  must  be  used. 

Characteristics.  —  Ordinary  ether  is  a  very  volatile  liquid 
with  a  peculiar  pleasant  odor.  It  boils  at  34.9°  C.  It  is 
an  excellent  solvent  for  fats,  oils,  and  various  other  organic 
bodies.  It  is  used  often  as  an  anaesthetic. 

Petroleum.  —  Petroleum  is  a  very  complicated  mixture 
of  hydrocarbons,  that  from  different  sources  varying 
greatly.  When  pumped  to  the  surface,  the  lower  mem- 
bers of  the  paraffine  series,  being  gases,  escape.  In  the 
process  of  refining,  the  light  oils,  rhigoline,  gasolene, 
naphtha,  benzine,  come  over  before  the  kerosene.  Later 
we  have  the  solid  paraffines  and,  in  some  cases,  a  residue 
of  asphaltum.  To  render  the  kerosene  safe  it  is  necessary 
that  the  lighter,  more  volatile  oils  be  carefully  removed 
by  distilling.  How  well  this  has  been  done  is  learned  by 
determining  the  "  flash  point "  of  the  oil. 

CARBOHYDRATES 

Thus  far  we  have  been  studying  hydrocarbons  and  their 
derivatives.  We  shall  now  consider  a  few  carbohydrates; 
that  is,  compounds  containing  hydrogen  and  oxygen  in 
such  proportions  as  to  form  a  certain  number  of  molecules 
of  water.  Among  these  may  be  named  the  simple  sugars, 
as  glucose  ;  the  complex  sugars,  as  cane  sugar ;  and  starch 
and  cellulose. 

Glucose        C6H12O6 

Cane  sugar        ....     ^12^22^11 

Starch (C6H1006)» 

Glucose.  —  Glucose  is  ordinarily  prepared  by  treating 
corn  starch  with  dilute  sulphuric  acid  and  removing  the 
excess  of  acid  with  calcium  carbonate.  The  solution  is 


372  MODERN    CHEMISTRY 

then  boiled  down  to  a  sirup  or  to  the  point  of  crystalliza- 
tion. The  sulphuric  acid  serves  as  a  catalytic  agent  and 
causes  the  starch  to  take  up  a  molecule  of  water,  as  shown 
by  the  following  equation  :  - 

C.H1008  +  H20  -*  C6H1306 

Starch  Glucose 

By  the  action  of  ferments,  as  already  stated,  cane  sugar 
may  be  changed  to  glucose  and  a  closely  allied  sugar, 
fructose,  thus:  — 

C12H22On  +  H20«-C6H1206  +  C6H1206 

Cane  sugar  Glucose  Fructose 

It  will  be  noticed  that  glucose  and  fructose  have  the  same 
formula;  but  glucose  turns  the  plane  of  polarized  light 
to  the  right,  while  fructose  turns  it  to  the  left.  Fructose 
is  about  as  sweet  as  cane  sugar,  while  glucose  is  only 
about  three  fifths  as  sweet. 

Cellulose,  (C6H1005)W.  —  Cellulose  belongs  to  the  same 
class  of  compounds  as  starch,  each  having  the  same  empir- 
ical formula.  It  is  the  basis  of  all  vegetable  fiber.  Flax, 
cotton,  hemp,  rags,  paper,  etc.,  consist  largely  of  cellulose. 
From  its  formula  and  what  has  been  said  about  the  prep- 
aration of  glucose,  it  will  be  readily  seen  that  any  of  the 
above  forms  of  cellulose,  or  sawdust,  for  example,  might  be 
converted  into  glucose.  The  chemical  action  induced  by 
sulphuric  acid  is  the  same  as  already  shown  in  the  inver- 
sion of  the  starch. 

Ethereal  Salts.  —  If  we  examine  the  formula  of  an  alco- 
hol, we  shall  see  that  it  resembles  somewhat  that  of  a 
metallic  hydroxide.  Thus  :  — 

C2H5HO        .     .     .     .       Ethyl  alcohol 
NaHO Sodium  hydroxide 

The  one  is  the  hydroxide  of  an  organic  radical,  the  other 


APPENDIX    D  373 

of  a  metal.  In  some  respects  other  than  in  the  one  named 
the  two  classes  of  compounds  are  similar.  As  has  been 
shown,  acids  may  react  with  the  alcohols,  forming  salts. 
For  example,  we  have  seen  — 

C2H5HO  +  H2S04  ->  C2H6HSO4  +  H2O. 
Such  compounds  we  often  call  ethereal  salts. 

Ethyl  Acetate,  C2H5C2H302.  —  This  compound,  also  called 
acetic  ether,  may  be  prepared  by  treating  alcohol  with 
acetic  acid,  as  shown  by  the  following  reaction  :  — 

C2H5HO  +  CHgCOOH  -*-  C2H5CH3COO  +  H2O. 

It  will  be  seen  that  the  reaction  is  similar  to  that  of  an 
alkaline  hydroxide  with  an  acid.  Ethyl  acetate  is  a  color- 
less, neutral  liquid,  of  a  rather  pleasant  odor,  with  a  boiling 
point  of  73°  C.  It  is  used  somewhat  as  a  medicine. 

Glycerine,  C3H5(HO)3. — Glycerine  is  a  triacid  alcohol; 
that  is,  an  alcohol  with  three  replaceable  hydroxyl  groups. 
It  is  a  by-product  of  the  manufacture  of  soap.  It  is  a 
familiar,  colorless,  sirupy,  sweet-tasting  liquid,  readily 
soluble  in  water. 

Glyceryl  Salts.  —  Such  fats  as  those  found  in  beef  and 
mutton  suet  and  others  are  mixtures  mainly  of  three  ethe- 
real salts,  in  which  glycerine  as  the  base  is  combined  with 
certain  fatty  acids.  For  example,  beef  fat  consists  mainly 
of  stearin,  palmitin,  and  olein. 

Stearin  .  .  .  C8H6(C17HMCOO)8 
Palmitin  .  .  .  C3H5(C15H31COO)3 
Olein  ....  C3H5(C17H33COO)3 

Saponification. — When  the  fats  are  treated  with  an 
alkali,  as  caustic  soda,  the  ethereal  salt  is  decomposed,  free 
glycerine  is  formed,  and  a  metallic  salt  of  the  organic  acid, 
known  as  soap.  Thus  :  — 


374  MODE11X    CHEMISTRY 

C3H6(C17H35COO)8  +  3  NaHO  ->  CSIIS(HO), 

Glycerine 

+  3  NaC17H35COO 

Soap  (sodium  stearate) 

Chemical  Action  of  Soap.  —  When  soap  is  dissolved  in 
water,  being  a  salt,  it  is  very  largely  ionized,  as  all  salts 
are.  At  the  same  time  some  molecular  sodium  hydroxide 
and  stearic  acid  will  form  from  union  with  the  ions  from 
the  water.  But  sodium  hydroxide,  being  a  strong  base,  is 
almost  completely  ionized,  while  stearic  acid,  being  exceed- 
ingly weak,  is  ionized  very  slightly.  Hence  we  have  pres- 
ent a  very  large  number  of  sodium  ions,  which  are  the 
active  principle  in  cleansing  by  such  soap.  When  soap  is 
put  into  hard  water,  the  salts  in  the  water  react  with  the 
soap,  forming  a  calcium  salt,  for  example,  with  the  organic 
acid.  This  is  a  compound  insoluble  in  water  and  it  ap- 
pears as  a  precipitate  upon  the  surface  of  the  water,  and 
we  speak  of  it  as  scum.  The  chemical  action  may  be  rep- 
resented thus :  - 

CaSO4  +  2  NaC17H35COO  ->  Na2SO4  +  Ca(C17H35COO)2 


APPENDIX  E 

PROBLEMS 
CHAPTER   VI 

1.  Find  the  molecular  weight  of  crystallized  zinc  sul- 
phate, which  contains  seven  molecules  of  water  of  crystalli- 
zation.    Also,  of  crystallized  magnesium  sulphate,  having 
the  same  amount  of  water. 

2.  In  5  g.  magnesium  sulphate  crystals  how  much  water 
of  crystallization  ? 

3.  How  many  grams  of  oxygen  can  be  obtained  from 
2  kg.  of  mercuric  oxide  ?     From  28  g.  of  water  ? 

4.  How  many  grams  of  sodium  hydroxide  can  be  pre- 
pared by  treating  20  g.  of  sodium  with  water  ? 

5.  To  prepare  50  1.  of  oxygen  at   standard   conditions 
how  much  potassium  chlorate  is  needed  ? 

6.  What   is   the  per    cent   of    oxygen    in    potassium 
chlorate  ? 

7.  How  much  crystallized  zinc  sulphate  could  you  pre- 
pare  by   dissolving    10   g.   of    zinc    in   dilute    sulphuric 
acid  ?    What  weight  of  hydrogen  would  be  set  free  at  the 
same   time  ?     What   would  be    its   volume  ?     (Standard 
conditions.) 

CHAPTER  VII 

1.  By  the  method  of  preparing  nitrogen  as  given  in 
Experiment  41,  page  73,  what  weight  of  sal  ammoniac  will 
be  needed  to  prepare  10  g.  of  nitrogen  ?  How  many 
liters  of  nitrogen  would  this  be,  if  nitrogen  is  14  times  as 
heavy  as  hydrogen  ? 

375 


376  MODERN    CHEMISTRY 

2.  How  much  common  salt  would  be  obtained  in  the 
above  experiment  ? 

3.  How   many  grams  of   ammonia  could  be   obtained 
from  1000  g.  of  ammonium  chloride  ?     How  much  slaked 
lime  would  be  needed  ? 

4.  What  weight  of   nitrous   oxide  could   be  prepared 
from  10  g.  of  ammonium  nitrate  ? 

5.  How  much  nitric  acid  could  be  prepared  from  50  g. 
of    sodium   nitrate  ?     How   much   sulphuric   acid   would 
be  needed  ? 

6.  How   much  water  in  one  ton  of   ferrous   sulphate 
(FeS04  .  7  H20)? 

CHAPTER   VIII 

In  the  proportion,  v  :  v°  :  :  t  :  £°,  where  v°  is  the  volume 
of  a  gas  at  zero  temperature,  if  we  substitute,  we  have 
273  v  =  v°  (273  +  0;  or 

v  =  v°  (1  +  1/273^) 
v  =  v°  (1  +  0.0036650. 

If  the  student  prefers,  he  may  use  this  expression  instead 
of  the  method  he  has  followed  on  page  96.  If  we  raise  the 
temperature  of  a  gas  without  allowing  it  to  expand,  we 
increase  the  pressure  in  the  same  proportion.  Hence  we 
may  substitute  p  and  p°  for  v  and  v°  in  the  above  formula. 
We  then  have  p=p°  (1  +  0.0036650- 


1.  If  the  gauge  of  a  steam  boiler  showed  a  pressure  of 
4  atmospheres,   what  would  be  the  temperature  of  the 
steam  contained  in  the  boiler  ? 

2.  If  a  balloon  rises  to  a  height  where  the  barometer 
registers  half  what  it  does  at  sea  level,  what  must  be   the 
temperature  of  the  atmosphere  if  the  gas  in  the  balloon 
has  not  changed  in  volume  ? 


APPENDIX    E  377 

3.  What  must  be  the  pressure  in  a  boiler  if  the  temper- 
ature has  been  sufficient  to  melt  the  fusible  plug,  point  of 
fusion  being  225°  C.  ? 

4.  If  a  boy  pumps  air  into  a  bicycle  tire,  already  filled 
under  a  pressure  of  760  mm.,  until  it  is  under  a  pressure 
of  5  atmospheres,  assuming  that  the  tube  does  not  expand, 
theoretically  how  much  would  the  air  rise  in  temperature  ? 

5.  A  certain  amount  of  potassium  chlorate  yielded  27.3 1. 
of  oxygen  in  a  room  where  the  barometer  read  740  mm. 
and  the  thermometer  23°.       What  would  be  the  volume 
under  standard  conditions  ?     (1 1.  O  =  1.43  g.) 

6.  I  collected  over  water  950  cc.  of  hydrogen  in  a  room 
at  a  temperature  of  25°  and  a  pressure  750;  find  the  true 
volume  of   gas  under  standard  conditions,  allowing   for 
aqueous  tension.     (See  page  404,  section  22.) 

7.  How  much  oxygen  should  I  obtain   from  5   g.  of 
potassium  chlorate,  collecting  over  water  in  a  room  at  a 
temperature  of  200°  C.  and  barometer  reading  740  mm.  ? 

8.  If  air  is  14.44  times  as  heavy  as  hydrogen  at  stand- 
ard conditions,  what  must  be  the  pressure  that  the  density 
may  be  the  same  as  that  of  hydrogen  ? 

9.  I  have  a  liter  flask  which  is  able  to  withstand  an 
internal   pressure    of   4   atmospheres.     It   is   filled   with 
oxygen  at  740  pressure  and  11°  C.     To  what  temperature 
must  the  gas  be  raised  to  cause  the  pressure  to  break  the 
flask  ? 

10.  A  liter  flask  is  filled  with  oxygen  under  normal 
temperature  and  pressure.      To  what  temperature  must 
the  gas  be  raised  to  lower  its  density  from  16  to  14  ? 
What  will  be  the  volume  of  the  gas  then  ? 

11.  To  what  temperature  must  a  volume  of  hydrogen 
be  raised  that  its  density  shall  be  one  half  what  it  is  at 
standard  conditions  ? 


378  MODERN    CHEMISTRY 

CHAPTER  IX 

1.  What  weight  of  chlorine  could  be  prepared  by  using 
50  g.  of  pyrolusite  (80  per  cent  MnO2)  with  strong  hydro- 
chloric acid  ? 

2.  What  weight  of  chlorine  is  needed  to  combine  with 
10  g.  of  hydrogen?     What  weight  of  hydrochloric  acid 
would  be  obtained  ? 

3.  What  is  the  greatest  weight  of  hydrochloric  acid 
that  could  be  prepared  from  50  kg.  of  common  salt  ? 

4.  How  much  bromine  would  be  set  free  from  a  solution 
of  potassium  bromide  by  means  of  5  g.  of  chlorine  ?     How 
much  iodine  from  potassium  iodide  ? 

5.  What   weight   of  iodine    could    be    obtained    from 
1  kg.  of  sodium  iodide  ?     How  much  manganese  dioxide 
would  be   needed  in   setting  the  iodide  free  by  the  usual 
method  ? 

6.  With  chemicals  at  the  following  prices,  manganese 
dioxide,  40  c.;  hydrochloric  acid,  36  per  cent,  8  c.;  com- 
mon salt,  1  c. ;    and  sulphuric  acid,  10  c.   per  pound,  — 
which  is   the   cheaper    method    of   making   chlorine  :  by 
using  manganese  dioxide  and  hydrochloric  acid,   or  from 
salt,  sulphuric  acid,  and  manganese  dioxide,  provided  the 
by-products  are  not  used  in  either  case  ? 

CHAPTER  XI 

1.  What  weight   of   carbon   dioxide   can   be  obtained 
from  1  ton  of  limestone,  80  per  cent  pure  ? 

2.  What  weight  of  calcium  chloride  would  be  obtained 
at  the  same  time  ? 

3.  If  60  kilos  of  marsh  gas  are  burned,  what  weight  of 
carbon  dioxide  and  of  watel*  would  be  obtained  ? 

4.  If  60  kilos  of  ethylene  are  burned,  what  weight  of 
air  would  be  necessary  for  perfect  combustion  ? 


APPENDIX    E  379 

5.  How  much  acetylene  can  be  obtained  from  5  Ib.  of 
calcium   carbide  ?     What  weight  of  calcium  hydroxide  ? 

6.  With  carbide  worth  10   c.   per  kilogram,  knowing 
acetylene  to  be  thirteen  times  as  heavy  as  hydrogen,  what 
would  be  the  cost  of  acetylene  per  liter  ? 

7.  If  the  equation,  3  C  +  SiO2  ->  2  CO  +  SiC,  represents 
the  preparation  of  carborundum  in  the  electric  furnace, 
what  weight  of  sand  is  necessary  to  prepare  500  kg.  of 
carborundum  ? 

8.  One  hundred  cubic  centimeters  of  water    at    0    C. 
and  one  atmosphere  pressure  will  dissolve  180  cc.  of  car- 
bon dioxide,  and   under  4  atmospheres,   720  cc.     If  you 
drink  a  glass  of  soda  water,  500  cc.,  with  the  temperature 
of  the  water  zero,  how  much  gas  would  you  drink  provided 
none  escaped  on  being  drawn  from  the  faucet,  assuming 
the  pressure  to  be  4  atmospheres  ?     What  would  be  the 
weight  of  the  gas  if  it  is  twenty-two  times  as  heavy  as 
hydrogen  ? 

9.  If  a  spherical  balloon,  8  m.   in  diameter  is    filled 
with  a  mixture  of  hydrogen  and  marsh  gas,  half  of  each, 
marsh  gas  being  eight  times  as  heavy  as  hydrogen,  what 
will  be  the  buoyancy  of  the  balloon  if  the  weight  of  the 
car  and  the  balloon  itself  is  10  kg.  ? 

10.  When  carbon  dioxide  is    passed   into    lirnewater, 
this   reaction   takes    place  :    Ca(HO)2  +  CO2—>CaCO3  + 
H2O.     If  20  1.  of  the  gas  are  passed  through  lime  water 
what  weight  of  dry  calcium  carbonate  would  be  obtained? 

11.  An  analysis   of   a   sample   of   coal   shows   that   it 
contains:   carbon,    83  per  cent  ;    hydrogen,    5  per  cent  ; 
sulphur,  1.5  per  cent;  oxygen  2.5  per  cent;  nitrogen  1 
per  cent ;  ash,  6  per  cent.     If  air  by  weight  is  23  per  cent 
oxygen,   how  much    air    by  weight    and    volume  will    it 
require  to  burn  1000  Ib.  of  the   coal  ?      Assume   that  the 


380  MODERN    CHEMISTRY 

hydrogen  burns  to  form  water,  the  carbon  to  carbon  dioxide, 
and  the  sulphur  to  sulphur  dioxide.  The  ash  and  nitrogen 
do  not  burn. 

CHAPTER    XII 

1.  In  Experiment  102,  page  160,  what  weight  of  salt 
should   be   obtained  from   the   one  gram  of  sodium  car- 
bonate ?     What   weight    if    dry    sodium  carbonate  were 
used  ? 

2.  In  Experiment  106,  page  164,  what  weight  of  copper 
nitrate    will  be  obtained  from   2|  g.  of  copper  ?     What 
weight   of   nitric    acid    theoretically    would    be    needed  ? 
What  should  be  the  weight  of  the  copper  oxide  obtained  ? 

3.  To  neutralize  500  cc.  of  hydrochloric  acid  made  to 
contain  3.65  g.   of  pure  acid  per  liter,  what  weight  of 
pure  sodium  hydroxide  would  be  needed  ? 

4.  I  used  50  cc.  of  sodium  hydroxide  solution,  made  to 
contain  4  g.  of  pure  hydroxide  in  100  cc.,  to  neutralize 
250  cc.  of  commercial  acetic  acid.     If  its  specific  gravity 
is  1.014,  what  is  the  strength  of  the  acid  (grams  in  100  g. 
of  acid)  ? 

5.  How  much  silver  nitrate  will  be  needed  to  precipi- 
tate the  chlorine  in  5.85  g.  of  common  salt  ? 

6.  If  I  dissolve  1.7  g.  of   silver   nitrate    in    1000    cc. 
pure  water  and  then  use  100  cc.  of  this  solution  to  precip- 
itate the  chlorine  in  500  cc.  of  spring  water,  how  many 
g.   of  salt,  assuming   the  chlorine   to    be   present  in  the 
form  of  salt,  would  there  be  in  a  liter  ? 

7.  What  weight  of  zinc  will  be  necessary  to  displace 
1  g.   of  hydrogen  from  sulphuric  acid  ?      From   hydro- 
chloric  acid  ? 

8.  What  weight  of  magnesium  would  be  needed   for 
the  same  purpose  ?     Of  aluminum  ? 


APPENDIX   E  381 

CHAPTER  XIH 

1.  What  weight  of   sulphur  could   be  obtained  from 
1000  kg.  of  iron  pyrites  if  heated  in  sealed  retorts  ? 

2.  What  weight  of  sulphur  dioxide  would  be  obtained 
from  1000  kg.  of  iron  pyrites  if  heated  with  plenty  of  air  ? 

3.  How  much  sulphuric  acid  could  be  prepared  from 
the  sulphur  dioxide  obtained  from  1000  kg.  of  pyrites  ? 

4.  How  much  air  in  grams  is  necessary  to  roast  the 
pyrites  for  the  sulphur  dioxide  in  problem  3,  if  air  is  14.5 
times  as  heavy  as  hydrogen  ?     It  may  be  assumed  that 
the  air  is  23  %   oxygen. 

5.  How  much  sodium  nitrate  is  necessary  to   prepare 
100  g.  of  nitric  acid  ?     What  weight  of  sulphur  dioxide 
would  this  amount  of  nitric  acid  oxidize  ? 

6.  For    every    kilogram    of    sulphur   used    in   making 
sulphuric  acid,  what  weight  of  sulphur  dioxide  would  be 
obtained  ?     What  weight  of  nitric  acid  would  be  neces- 
sary to  oxidize  it  ?     What   weight    of   sulphur   trioxide 
would  be  obtained  ?     What  weight  of   steam  would   be 
required  to  convert  the  trioxide  to  sulphuric  acid  ? 

CHAPTER   XVI 

1.  This  equation  has  been  found  to  be  true  : 

2  mol.  hyd.  -f- 1  mol.  oxy.  — >  2  mol.  water, 
or  2H2  +  02-^2H20. 

If  100  cc.  of  hydrogen  are  exploded  with  the  required 
amount  of  oxygen,  what  volume  of  steam  would  be  pro- 
duced ? 

2.  It  has  been  found  that  H2+Cl2-»2  HC1.     If  one 
liter  of  hydrogen  is  exploded  with  the  necessary  amount 
of  chlorine,  what  volume  of   hydrogen   chloride  will   be 
obtained  ? 

3.  This  equation  is  true  :    3  H2  +  N2->  2  NH3.     What 


382  MODERN    CHEMISTRY 

volume  of  hydrogen  is  required  to  combine  with  100  cc.  of 
nitrogen  ?  What  volume  of  ammonia  would  be  obtained  ? 
The  above  problems  illustrate  the  Law  of  Simple 
Volumes;  that  is,  that  the  volumes  of  gases  combining 
with  one  another  always  bear  some  simple  ratio  to  each 
other  and  to  the  resulting  product,  if  that  product  is 
gaseous. 

4.  To   produce   as   above   2000  cc.   of  ammonia  what 
volume    of    nitrogen    is   necessary  ?       What    volume    of 
hydrogen  ? 

5.  To   produce   1000   cc.   of  hydrogen  chloride,  what 
volume  of  chlorine  is  needed  ?     Of  hydrogen  ? 

6.  To  produce  2000  1.  of  steam,  what  volume  of  hydro- 
gen is  required  ?     What  of  oxygen  ? 

7.  What  volume  of  hydrogen  would  be  set  free  from 
sulphuric  acid  by  12  g.  of  magnesium  in  a  room  at  0°  C.  ? 
How  much  at  a  temperature  of  20°  C.  ?     (Pressure  normal 
in  both  cases.) 

8.  What  would   be  the  volume  of  acetylene  obtained 
from  1000  g.  of  carbide  if  the  barometer  reads  740  and 
the  thermometer  zero  ? 

9.  What  would  be  the  volume  of  the  carbon  dioxide 
obtained  by  burning  1000  g.  of  coal,  80  per  cent  carbon,  if 
volume  is  estimated  at  20°  C.  and   the  barometer  reads 
750? 

NOTE.  —  It  has  been  found  that  22.32  1.  of  hydrogen  at  standard 
conditions  weigh  2  g.,  or,  as  it  is  spoken  of  in  the  chapter  on  Solution, 
a  gram-molecule.  In  the  same  way,  according  to  Avogadro's  Law, 
the  same  volume  of  any  gas,  22.32  1.,  should  weigh  a  gram-molecule 
of  that  gas.  This  is  found  to  be  true.  Thus,  22.32  1.  of  oxygen 
weigh  32  g. ;  22.32  1.  of  carbon  dioxide  weigh  44  g. ;  etc.,  —  all  being 
estimated  under  normal  conditions. 

10.  In  problem  1  above,  if  22.32  1.  of  hydrogen  are 
used,  what  volume  of  oxygen  would  be  needed  ? 


APPENDIX    E  383 

11.  In  problem  3,  33.48  1.  of  hydrogen  would  require 
what  volume  of  nitrogen  ? 

12.  If  3.5  1.  of  oxygen  are  mixed  with  1.5  1.  of  marsh 
gas  and  exploded,  what  volume  of   carbon   dioxide  will 
be   formed  ?      What   of   steam,  and  how   much   oxygen 
will  remain  ? 

13.  What  volume  of  air,  21  per  cent  oxygen,  will  be 
needed  to  completely  burn  50  1.  of  ethylene,  and  what 
will  be  the  volume  of  the  carbon  dioxide  which  will  be 
formed  ? 

14.  Determine  the  same  in  the  case  of  acetylene. 

GENERAL   PROBLEMS 

1.  In  the  process  of  analyzing  a  sample  of  flint  glass 
the  lead  contained  was  converted  into  lead  sulphate  ;  3  g. 
of  the  glass  gave  1.25  g.  of  lead  sulphate.     Find  the  per 
cent  of  lead  oxide  in  the  glass. 

2.  A    specimen    of   dolomitic    limestone,   calcium   and 
magnesium  carbonate,  was  found  to  contain  5  per  cent  of 
silica.     If  a  hundred  pounds  of  the  sample  yielded  43.07 
Ib.  of  carbon  dioxide,  what  were  the  per  cents  of  calcium 
and  magnesium  carbonate  in  the  sample  ? 

3.  A  mixture  of  silver  chloride  and  bromide  weighing 
2  g.  was  heated  and  a  stream  of  chlorine  passed  over  it ; 
when  cooled  and  weighed  again,  it  showed  a  loss  of  .3  g. 
What  per  cent  of  the  mixture  was  silver  chloride  ? 

4.  According  to  Dulong  and   Petit's  Law  uall  atoms 
have  the  same  capacity  for  heat."     This  means  that  the 
atomic  weight  of  any  element  multiplied  by  its  specific 
heat  is  a  constant    quantity.      For  example,  the  specific 
heat  of  iron  is  0.114;  its  atomic  weight  is  56.      The  prod- 
uct of  these  two  factors  is  6.384.     This  product  for  all 
the  elements  is  approximately  6.4  and  is  called  the  atomic 


384  MODERN    CHEMISTRY 

heat  of  the  element.     The  specific  heat  of  lead  is  0.0315. 
Determine  its  atomic  weight. 

5.  The    specific    heat    of    arsenic    is    0.083  ;    of    zinc, 
0.0955  ;  of  platinum,  0.0325.     Find  their  atomic  weights. 

6.  The  atomic  heat  of  bromine  is  6.7;  of  iodine,  6.87; 
of  calcium,  6.8.     Find  their  specific  heats. 

7.  The  specific  heat  of  magnesium  is  0.25.     How  does 
this  show  that  the  atomic  weight  is  24  and  not  12  ? 


APPENDIX  F 

LABORATORY  SUGGESTIONS 

1.  Neatness.  —  To  the  best  success  in  any  chemical 
experiment  neatness  is  absolutely  essential;  indeed,  the 
merest  traces  of  substances  foreign  to  those  with  which  we 
are  working  may  cause  a  complete  failure  of  the  experi- 
ment. A  student  hardly  knows  what  neatness  is  until  he 
has  had  a  thorough  training  in  chemical  analysis. 

The  apparatus  should  always  be  clean  when  put  away, 
and  then  before  using  should  be  rinsed  with  pure  water. 
Never  lay  a  cork  or  stopper  down  upon  the  table,  as  it  will 
gather  dust  and  thus  pollute  the  reagent.  If  you  desire 
to  use  some  solution  contained  in 
a  bottle,  take  the  stopper  between 
the  first  and  second  fingers  with  the 
palm  of  the  hand  upward  and 
remove  it  from  the  bottle  ;  then 
without  laying  it  down  seize  the 
bottle  with  the  thumb  on  one  side 
and  the  fingers  on  the  other.  In 
this  way  the  stopper  will  not  come  in  contact  with  the 
side  of  the  bottle  and  soil  it,  neither  will  dust  and  dirt 
be  gathered  from  the  table.  The  reagent  bottles  should 
be  frequently  wiped,  as  they  soon  become  more  or  less 
covered  with  deposits  which  form  from  the  gases  gener- 
ated in  the  laboratory.  The  table  also  should  be  kept 
«lean,  and  water  and  other  liquids  should  not  be  allowed 
to  remain  if  accidentally  spilled. 

385 


386  MODERN  CHEMISTRY 

2.  Order. —  Great  advantage  will  also  be  secured  by 
having  everything  in  its  allotted  place.  Especially  is  this 
true  of  the  reagent  bottles,  and  the  more  there  are  of 
these  the  more  important  it  is  that  they  should  be  kept 
in  order.  For  the  larger  schools  probably  about  twenty 
reagent  bottles  will  be  furnished  each  student,  and  these 
will  be  arranged  upon  two  shelves,  one  above  the  other. 
In  such  case,  the  following  order  is  suggested  as  being  as 
good  as  any  :  — 

LOWER  SHELF 

Beginning  at  left  hand  :  — 

Sulphuric  Acid      .         .         Hydric  Sulphate      .         .  H2SO4 

Hydrochloric  Acid          .         Hydric  Chloride       .         .  HC1 

Nitric  Acid    .         .         .         Hydric  Nitrate         .         .  HNO3 

Ammonium  Hydroxide  or  Hydrate       ....  NH4OH 

Ammonium  Chloride NH4C1 

Ammonium  Sulphide    .......  (NH4)0S 

Ammonium  Carbonate          ......  (NH4)2CO3 

Barium  Chloride BaCl2 

Potassium  Dichromate  .         Potass.  Acid  Chromate    .  K2Cr2O7 

Potassium  Ferrocyanide K4FeCy6 

UPPER  SHELF 

Calcium  Hydroxide  or  Hydrate     .....  Ca(OH)2 

Mercuric  Chloride          .......  HgCl2 

Silver  Nitrate         .         .         Argentic  Nitrate       .         .  AgNO3 

Ferric  Chloride      ........  Fe2Cl6 

Acetic  Acid    .         .         .         Hydric  Acetate         .         .  HC2H3O2 

Lead  Acetate          .         .         Plumbic  Acetate       .         .  Pb(C2H3O.2)2 

Potassium  Iodide  ........  KI 

Sodium  Carbonate          .         Crystals  or  powder  .         .  Na2CO3 

Borax,  powdered Na2B4O7 

Some  of  the  above  reagents  are  known  by  different 
names,  and  in  such  cases  two  of  them,  the  most  common, 
have  been  given  above. 


APPENDIX  F  387 

3.  Apparatus  needed.  —  Each  student  should  be  assigned 
a  locker  where  he  may  safely  keep  the  apparatus  supplied 
to  him,  and  for  the  care  of  this  he  should  be  held  respon' 
sible.  The  following  apparatus  is  suggested :  — 

3  Test-tubes,  5  x  f.  1  Test-tube  Brush. 

3  Test-tubes,  6  x  $.  1  Pair  Forceps. 

3  Test-tubes,  6  x  f.  1  Glass  Stirring  Rod, 

1  Evaporating  Dish,  small.  1  Blowpipe. 

1  Evaporating  Dish,  medium.  1  Platinum  Wire. 

1  Beaker,  2  oz.  1  Rubber  Cork,  one  hole. 

.      1  Small  Flask,  2£  oz.  1  Rubber  Cork,  two  holes. 

1  Delivery  Tube.  1  Small  Mortar. 

Directions  will  be  given  later  for  preparing  the  delivery 
tube,  stirring  rod,  and  some  other  desirable  apparatus. 

The  student  should  also  have  the  following,  and  will 
furnish  them  himself  :  — 

An  apron,  reaching  to  the  ankles.     This  may  be  made 
of  denim,  oil  cloth,  or  rubber  cloth.     The  last  is  the  most 
serviceable  in  many  ways,  but  is  the  most  expensive. 
A  Towel.  An  Iron  Spoon. 

A  Bar  of  Soap.  A  Clay  Pipe. 

A  Small  Magnet.  A  Candle. 

A  Small  Triangular  File. 

The  candle  will  be  needed  very  frequently  during  the 
first  half  of  the  work  in  studying  the  properties  of  gases. 
Common  Property.  —  In  addition  to  the  individual  prop- 
erty assigned  above,  certain  articles  on  account  of  their 
size  or  for  other  reasons  are  used  in  common.  There 
should  be  enough  of  them  so  that  each  member  of  the  class 
may  be  supplied.  Among  these  may  be  named  ;  — » 

An  Iron  Pan,  8  x  14  and  about  2J  inches  (Jeep,  to,  b§ 
used  for  a  pneumatic  trough. 


388  MODERN  CHEMISTRY 

Test-tube  Rack.  Iron  Ring-stand. 

Bunsen  Burner,  with  Con-  Funnel. 

nections.  Wash-bottle  (?). 

Wire  Gauze.  Sand  Bath. 

MANIPULATIONS 

4.  Cutting  Glass.  —  To  cut  tubing,  with  a  sharp-cornered 
file  scratch  the  glass  somewhat  deeply  where  you  desire  to 
cut  it.     Now  grasp  the  tube  with  both  hands,  the  fingers 
above,  and  the  thumbs  below  nearly  meeting  at  the  line 
scratched  by  the  file.     Now  bend  the  tube  downward  and 
pull  strongly  apart  at  the  same  time.     With  a  little  prac- 
tice good  square  cuts  may  be  made.     The  rough  ends  thus 
secured  will  cut  any  rubber  connections  used.     To  prevent 
this  hold  them  in  the  Bunsen   flame  until  the  glass  by 
becoming  softened  loses  its  sharp  edges. 

Sometimes  it  becomes  necessary  to  cut  a  bottle  or  large 
tube  in  two  ;  this  may  be  done  in  two  ways,  but  both  de- 
pend upon  the  unequal  heating  of  the  glass.  Tie  around 
a  bottle  where  you  desire  to  cut  it  an  ordinary  twine 
string ;  saturate  it  with  kerosene  and  ignite  it.  Some- 
times it  will  be  found  necessary  to  apply  the  oil  the  second 
time,  as  soon  as  the  first  has  ceased  to  burn,  and  again  ignite 
it.  In  this  way,  if  the  oil  has  been  applied  carefully,  a  nar- 
row line  extending  around  the  bottle  is  heated  strongly, 
and  if  the  glass  be  cooled  suddenly  by  pouring  over  it  cold 
water,  the  bottle  will  be  neatly  severed. 

5.  To  prepare  a  Delivery  Tube.  — This  may  be  made  of 
rubber  and  glass  tubing,  or  of  glass  alone.     The  former  is 
often  preferable  because  it  allows   of   more  freedom    in 
manipulation.     If  made  entirely  of  glass,  two  bends  are 
necessary,  and  one  should  be  within  an  inch  of  the  end. 
Hold  the  tubing  in  the  Bunsen  burner,  moving  it  back 


APPENDIX  F 


389 


FIG.  70. 


and  forth  and  rolling  it  around  so  as  to  warm  all  por- 
tions equally.  When  the  glass  begins  to  soften,  allow 
its  own  weight  to  bend  it,  and  take 
care  that  you  do  not  form  a  right- 
angled  tube,  but  one  of  a  gentle 
curve  like  the  elbow  of  a  stove  pipe. 
When  the  bend  has  cooled  just  a 
little,  close  the  openings  at  the  bot- 
tom of  the  burner  and  hold  the  glass 
in  the  luminous  flame  until  it  is  well 
covered  with  soot.  This  will  cause 
the  glass  to  cool  slowly  and  hence 
make  it  less  liable  to  fracture.  Com- 
plete by  making  the  second  bend  in 
the  same  way,  forming  an  obtuse  angle  as  shown  in  the 
figure.  If  rubber  connections  are  used,  a  second  bend 
is  unnecessary. 

6.  To  make  a  Jet.  —  Frequently  a  tube  drawn  to  a  fine 
point  is  desirable.       Take  a  piece  of  glass   tubing  5  or 
6  inches  in  length  and  heat  as  in  making  a  delivery  tube. 
When  it  begins  to  soften,  draw  it  slowly  apart  until  a 
tube  of  small  diameter  is  obtained  at  the  center,  as  shown 

„ in   a   in   the  adjoining 

figure.  When  some- 
what cooled,  cut  in  two 
at  a  ;  then  make  a  bend 
in  one  of  the  shorter 
FlG-  TL  tubes,  as  shown  ir>  b. 

Round  off  the  sharp  edges  and  anneal  as  previously  de- 
scribed. You  will  now  have  two  jets,  one  straight  and 
one  bent,  for  both  of  which  you  will  find  uses. 

7.  To  make  a  Wash-bottle.  —  Any  good-sized  bottle  or 
flask  will  do  for  this.     The  tube,  a,  should  be  drawn  to  a. 


390  MODERN  CHEMISTRY 

jet  as  shown  in  the  figure,  and  after  being  bent  should 
reach  nearly  to  the  bottom  of  the  flask.  The  other  tube 
after  being  bent  should  just  reach  through  the  cork.  By 
blowing  through  £>,  a  jet  of  water  may  be 
directed  wherever  desired;  or  if  a  larger 
stream  is  desired,  it  may  be  poured  out  at  b. 
The  bottle  is  more  convenient  if  the  jet,  a,  is 
attached  to  the  rest  of  the  tube  by  a  rubber 
tube  2  or  3  inches  long ;  the  stream  of  water 
may  then  be  turned  readily  in  any  direction. 
The  wash-bottle  is  indispensable  for  qual- 
itative work  in  washing  precipitates.  A 
rubber  band  should  be  slipped  over  the 
lower  end  of  the  tube,  a,  so  that  if  it  strikes  the  side  of 
the  flask  in  removing  the  cork  and  tubing  it  will  not 
be  broken.  If  the  lockers  are  too  small  to  receive  the 
wash-bottle,  one  may  be  used  in  common  by  the  students 
working  at  each  laboratory  table  or  section.  In  such  case 
it  is  better  for  each  student  to  have  a  short  tube  with  rub- 
ber connections  to  attach  to  6,  whenever  he  desires  to  use 
the  bottle. 

8.  To  repair  a  Test-tube. — Test-tubes  are  frequently 
broken  by  the  beginner,  but  they  may  be  easily  mended, 
and  will  then  be  almost  as  useful  as  at  first.  Hold  the 
broken  end  in  a  hot  Bunsen  burner  flame,  roll  the  tube 
about  to  heat  all  sides  evenly.  When  the  glass  becomes 
soft,  by  means  of  a  glass  rod,  which  will  cohere  to  the 
softened  tube,  draw  off  the  viscous  portion,  and  thus  seal 
the  tube.  Usually  a  small  mass  of  softened  glass  will  re- 
main upon  the  end  of  the  tube.  This  must  be  drawn  off 
in  the  same  way,  until  the  bottom  is  very  thin,  like  the 
rest  of  the  tube.  Then  by  alternately  heating  and  blow- 
ing into  the  tube,  it  may  be  rounded  out  and  made  almost 


APPENDIX  F  391 

as  perfect  as  a  new  tube.     After  a  little  practice  students 
may  become  skillful  at  this  work. 

9.  Blowpipe  Work.  —  In  metallurgy,  the  blowpipe  must 
be  used  frequently,  and  two  kinds  of  flames  are  employed, 
the  reducing  and  the  oxidizing.  In  preparing  for  either 
one,  turn  down  the  jet  to  about  a  quarter  its  usual  force, 
or  until  you  have  a  flame  not  much  larger  than  that  of  a 
good-sized  candle,  and  close  the  openings  at  the  bottom  so 
as  to  render  it  luminous.  In  the  figure,  a  shows  the  small 
luminous  flame  ready  for  the  use  of  the  blowpipe,  6  shows 
the  reducing  flame.  The  tip  of  the  blowpipe  is  placed 


FIG.  73. 


in  the  outer  edge  of  the  flame,  and  a  gentle  but  steady 
stream  of-  air  forced  into  the  flame.  In  this  way  a  small 
luminous  cone,  ?,  will  remain  in  about  the  center  of  the  flame, 
and  in  this  the  metallic  oxide  should  be  held.  This  lumi- 
nous portion  contains  red-hot  particles  of  carbon,  and  they 
have  the  power  of  reducing  oxides  of  metals  to  the  metallic 
condition.  If  this  luminous  cone  is  not  apparent,  too  much 
air  is  being  forced  into  the  gas.  Either  blow  more  gently, 
or  turn  the  gas  on  a  little  stronger.  With  a  little  practice 
the  student  will  learn  to  breathe  and  blow  at  the  same  time, 
and  will  not  find  the  work  especially  tiresome. 

For  the  oxidizing  flame,  (?,  above,  the  tip  of  the  blowpipe 
is  placed  in  the  very  center  of  the  jet.  In  this  way  the 
air  introduced  and  the  gas  become  thoroughly  mixed,  and 
complete  combustion  ensues.  The  cone  should  be  perfectly 


392 


MODERN  CHEMISTRY 


FIG.  74.  —  Collecting  over  water. 


non-luminous,  and  the  metal  to  be  oxidized  should  be  held 
about  where  n  is  in  the  cut.  The  flame  is  exceedingly  hot, 
and  having  an  excess  of  oxygen  readily  converts  into  oxides 
such  metals  as  are  oxidizable. 

10.  Collecting  Gases.  —  There  are  several  methods  for 
collecting  gases,  varying  according  to  the  characters  of  the 

gases.  Those  which  are 
insoluble  in  water  are  usu- 
ally collected  over  water. 
Students  will  find  an  or- 
dinary baking  pan,  2 
inches  deep  and  about  6 
inches  broad  by  12  long, 
sufficiently  large.  The 
bottle  to  receive  the  gas 
is  first  filled  with  water 
and  inverted  over  the  pan,  Fig.  74.  This  is  done  by 
holding  tightly  a  sheet  of  paper  or  glass  over  the  mouth 
of  the  bottle  until  inverted  and  placed  under  the  water 
in  the  pan.  The  delivery  tube,  T,  dips  under  the  bottle 
and  conducts  the  gas  from  the  generating  flask,  6r,  into  the 
bottle. 

11.  Collecting  by  Downward 
Displacement. — Gases  soluble  in 
water  obviously  cannot  be  col- 
lected  by  the  method  already 
described.      If   it   is   necessary 
to  have  them   absolutely  pure, 
mercury   is    frequently   substi- 
tuted for  the  water.     Ordina- 
rily, however,  if  heavier  than  air 

they  are  collected  by  downward  displacement.  By  this 
method  the  bottle  is  simply  left  standing  upon  the  table, 


FIG.  75. 


APPENDIX  F 


393 


and  the  delivery  tube  reaches  down  into  the  bottle. 
Thus  the  heavier  gas  is  introduced  below  the  air,  and 
gradually  displaces  it.  Such  gases  as  chlorine  or  carbon 
dioxide  are  collected  in  this  way.  If  the  gas  is  lighter 
than  air  and  soluble  in  water,  it  is  usually  collected  by 
upward  displacement.  The  receiving  bottle  is  held  in  an 
inverted  position,  and  the  delivery  tube  runs  up  to  the 
bottom  of  the  bottle,  gradually  displacing  the  air  in  the 
bottle.  In  Fig.  75,  a  shows  the  arrangement  for  collect- 
ing by  downward  displacement,  and  6,  that  for  upward 
displacement. 

12.  Measurements.  —  Frequent  reference  is  made  through- 
out this  work  to  the  cubic  centimeter  and  gram,  and  the 
student  should  have  fairly  definite  ideas 
of  these  terms.  This  can  come  only  by 
practice.  For  the  volumetric,  a  test-tube 
and  beaker  may  be  graduated.  From  a 
burette  run  into  a  test-tube  1  cc.  of  water  ; 
indicate  its  height  by  fastening  upon  the 
tube  just  above  the  lowest  part  of  the 
meniscus  a  narrow  strip  of  mucilage  paper. 
Add  another  cubic  centimeter  and  mark 
the  height  in  the  same  way.  Thus  grad- 
uate the  tube  up  to  5  cc.  ;  mark  it  also 
for  the  10  cc.  Now  that  the  graduation  lcc 
may  be  permanent,  with  a  file  scratch 
carefully  the  marks,  after  which  the  paper 
may  be  removed  ;  a  shows  the  meniscus 
for  each  cubic  centimeter,  and  b  the  small  strip  of  paper. 
In  the  same  way  graduate  a  beaker  for  5,  10,  15,  20,  and 
25  cc. 

As  different  compounds  vary  so  greatly  in  density,  it  is 
more  difficult  to  obtain  an  accurate  idea  of  a  gram,  but  the 


FIG 


394  MODERN  CHEMISTRY 

student  should  be  able  to  approximate  it.  Put  upon  one 
scale  pan  of  a  balance  a  small  evaporating  dish,  and  coun- 
terbalance it  with  shot  or  sand  upon  the  other.  Then  add 
a  gram  weight  to  the  shot.  Into  the  evaporating  dish  now 
slowly  add  common  salt  until  the  gram  weight  is  balanced. 
Thus  try  some  other  amount,  as  2  g.  or  5  g. 

If  the  classes  are  large,  one  portion  may  be  graduating 
the  test-tubes  and  beakers,  while  another  is  doing  the 
gravimetric  work.  This  will  greatly  expedite  matters. 

13.  Precipitates.  —  A    precipitate  is    any  solid   matter 
thrown  down  in  a  solution  by  adding  to  it  some  reagent. 
It  may  be  very  dense,  so  as  to  be  quite  jelly-like,  or  it  may 
form  merely  a  cloud  in  the  solution.      To  illustrate,  put 
one  drop  of  sulphuric  acid  into  a  beaker  half  or  two-thirds 
full  of  water  and  add  2  or  3  cc.  of  barium  chloride  solution. 
The  dilute  solution  should  thus  give  a  slight  precipitate 
only.     Now  powder  about  a  gram  of  ferrous  sulphate  and 
dissolve  in  as  little  water  as  possible,  2  or  3  cc.,  then  add 
a  few  drops  of  ammonia.     A  thick  gelatinous  precipitate 
should  form. 

14.  Decanting  and  Filtering.  —  These  are  processes  for 
separating  a  precipitate  from  the  solution  in  which  it  is 
formed.     When  the  precipitate  is  one  that  has  considerable 
density  and  settles  quickly,  leaving  a  clear  solution,  this 
supernatant  liquid  may  be  decanted  or  poured  off.     There 
is  no  objection  to  this  method  unless  the  presence  of  small 
particles  of  the  precipitate  in  the  decanted  portion,  or  of 
the  solution  in  the  precipitate,  will  interfere  with  subse- 
quent tests.     To  illustrate,  a  solution  of  lead  acetate  may 
be  precipitated  with  hydrochloric  acid,  and  after  warming 
slightly  and  allowing  the  precipitate  to  settle,  the  solution 
may  be  decanted. 

But  in  cases  where  the  separation  must  be  complete, 


APPENDIX   F 


395 


Folded  Twice         Opened 


FIG.  78. 


filtration  is  necessary,  that  is,  passing  the  solution  through 

a  filter  paper.     There  are  two  ways  of  folding  filters  :  the 

simplest,    and     one     used 

when  the  precipitate  is  to 

be  removed  from  the  pa- 

per, is  as  follows  :  fold  the 

paper  to  form  a  semicircle, 

&,    then    this    to    form    a 

quadrant,  making  one  fold 

slightly  smaller  than  the  other.  This  is  done  because 

funnels  are  seldom  perfectly  made, 
and  one  "quarter"  will  fit  them 
better  than  another.  Usually  this 
is  the  larger.  Now  open  out  one 
of  the  quarters,  and  press  down 
neatly  into  the  funnel.  If  the 

quarter  tried  does  not  seem  to  fit,  the  other  one  may  do 

so  better.     Now  moisten  with  a  little  water,  and  with  the 

fingers     press     the    paper 

against    the    sides   of   the 

funnel  to  remove  any  air 

bubbles     that    may    exist 

there.      In  filtering,   pour 

in  slowly  at  first,  especially 

if   the  precipitate  is  very 

finely  divided.    If  the  solu- 

tion does  not  come  through 

clear,  it  may  be  necessary 

to  filter  again  through  the 

same    filter    paper.      The 

pores    will    soon    become 

partially  filled,  and  the  fil- 


Dliiillillll 


trate  will  be  perfectly  clear. 


FIG.  79. 


306  MODERtf  CHEMISTS? 


In  filtering,  the  stem  of  the  funnel  should  always  be  made 
to  touch  the  side  of  the  beaker  or  vessel  into  which  the 
liquid  is  being  passed,  so  that  no  drops  may  spatter  out. 
Furthermore,  in  pouring  a  liquid  from  any  vessel,  it 
should  always  be  allowed  to  run  down  a  moistened  stir- 
ring rod  into  the  funnel.  By  observing  these  precautions, 
neatness  in  transferring  liquids  from  one  vessel  to  another 
will  be  secured, 

15.  Opening   Bottles.  —  The    common    acids    and   aqua 
ammonia,  as  well  as  some  other  reagents,  are  frequently 
put  up  in  bottles  with  glass  stoppers.     They  are  sealed  by 
dipping  the  stopper  into  melted  paraffin  before  inserting 
into  the  bottle.     To  remove  the  stopper  the  paraffin  must 
be  melted.     This  may  be  done  by  turning  down  the  gas- 
jet  moderately  low,  taking  the  bottle  in  both  hands,  hold- 
ing the  neck  over  the  flame,  not  too  close,  and  rolling  it 
rapidly  around  so  as  to  heat  all  sides  alike.     Be  careful  to 
heat  the  glass  only  gently.     In  a  moment  or  two  the  wax 
will  be  melted  and  the  stopper  may  be  very  easily  removed. 
With  a  little  practice  bottles  may  be  opened  in  this  way 
without  ever  breaking  or  cracking.     Be  careful,  however, 
in  removing  the  stopper,  never  to  have  the  face  directly 
over  the  bottle. 

16.  Platinum  Wires.  —  These  are  used  in  making  flame 
and  borax-bead  tests  for  various  metals.     For  the  sake  of 
convenience  in  handling,  they  are  generally  fused  into  a 

short  piece  of  glass  tub- 
ing.    Take  a  few  inches 
of  small-size  tubing  and 
FlG>  80*  draw  out,  as  in  making 

a  jet  such  as  has  already  been  described  for  use  in  testing 
the  combustibility  of  gases.  Cut  the  glass  in  two,  as 
before,  and  insert  the  platinum  wire  into  the  tubing  to 


APPENDIX  F 


397 


a  distance  of  3  or  4  cm. ;  again  hold  in  the  flame  until 
the  glass  is  softened.  Upon  cooling,  the  wire  will  be 
securely  fastened  in  the  tubing.  (See  Fig.  80.) 

17.  Electrolytic  Apparatus.  —  If  necessary,  the  student 
may  prepare  his  own  apparatus  for  experiments  in  electrol- 

yS*S  °ut  °^  ot^er  aPParatus  that 
he  will  find  at  hand.  Take  two 
pieces  of  heavy  platinum  wire, 
each  about  a  foot  long,  and  make 
into  spiral  coils  by  wrapping 
around  a  pencil.  Leave  two  or 
three  inches  straight  at  one  end, 
as  shown  at  a,  Fig.  81. 

Fit  to  a  short-necked  bell  jar 
with  an  open  top  a  rubber  cork 
with  two  small  holes,  and  support 
the  bell  jar  upon  an  iron  ring- 
stand,  fastening  it  securely  in 
position.  Next,  take  two  pieces 
of  small  glass  tubing,  each  long 
enough  to  reach  through  the  cork 
0,  and  extend  just  into  the  body  of  the  jar.  Insert  the 
straight  ends  of  the  two  platinum  spirals,  already  made, 
through  these  tubes,  and  fuse  the  glass  at  the  ends  so  as  to 
fasten  the  wires  firmly  in  the  glass ;  make  a  small  loop  in 
the  wire  at  the  lower  end.  See  b  in  the  figure.  Insert 
the  two  electrodes  thus  prepared  through  the  holes  in  the 
cork,  and  see  that  everything  is  water  tight. 

Next  take  two  burettes  with  glass  stop-cocks  and  deter- 
mine accurately  the  capacity  of  each  below  the  point  of 
graduation,  that  is,  from  m  to  n  in  Fig.  82.  This  must 
be  done  if  we  desire  to  measure  accurately  the  amount 
of  gas  collected.  Now  by  means  of  clamps  support  these 


FIG.  81. 


398 


MODERN  CHEMISTRY 


FIG.  82. 


two  burettes  inverted  over  the  two  spiral  electrodes,  and 
the  apparatus  is  complete.  For  use,  fill  the  bell  jar  with 
the  liquid  to  be  electrolyzed  to  some  distance 
above  the  mouth  of  the  burettes.  Attach  a 
rubber  tube  to  the  tip  of  the  burettes,  open  the 
stop-cock,  and  by  suction  fill  each  with  the  liquid 
and  close  the  stop-cock.  Turn  on  the  current, 
and  the  capacity  of  each  burette  above  the  point 
of  graduation  having  been  determined,  the 
amount  of  gas  which  collects  in  each  tube  is 
quickly  read. 

Instead  of  the  burettes,  test-tubes  8  inches  by  one-half 
in  diameter  may  be  used  with  good  results,  except  that 
the  gases  cannot  be  accurately  measured. 

18.  A  Simple  Electrolytic  Apparatus. — Occasionally  it 
may  be  desired  to  electrolyze  a  substance  without  sepa- 
rating the  gaseous  products.  For  such  purposes  a  very 
simple  form  of  apparatus  may  be  employed,  as  shown  in 
the  figure.  Prepare  the  two  electrodes  as 
described  for  the  more  complicated  form, 
and  fit  them  to  a  3-hole  stopper  as 
shown  in  Fig.  83.  Through  the  other 
opening  pass  a  bent  delivery  tube,  T,  for 
conducting  off  the  mixed  gases  which  will 
collect  in  the  top  of  the  bottle  when  the 
current  is  passed. 

Such  apparatus  as  this  may  be  used  to 
show  the  explosive  character  of  the  mix- 
ture of  hydrogen  and  oxygen  obtained  by 
the  electrolysis  of  water,  or  of  hydrogen  and  chlorine 
resulting  from  the  decomposition  of  hydrochloric  acid. 
To  prevent  the  contents  of  the  bottle  becoming  too  warm, 
it  should  be  placed  in  a  vessel  of  cold  water.  Use  hydro- 


FIG.  83. 


APPENDIX   F 


399 


chloric  acid  of  specific  gravity  about  1.1,  and  allow  the 
current  to  pass  for  some  time  before  collecting  the  gases, 
in  order  that  the  liquid  may  become  saturated  with  the 
chlorine.  If  it  is  desired  to  collect  bottles  of  the  mixed 
gases  over  water,  let  the  water  be  first  saturated  with 
common  salt. 

19.  Eudiometers.  —  The  eudiometer  is  an  instrument 
used  to  test  the  composition  of  mixed  gases.  The  most  con- 
venient form  for  all  purposes  is  the  U-shaped  one,  in  which 
mercury  is  used  to  confine  the  gases.  The  air  left  in  one 
limb  of  the  tube 
serves  as  an  air  cush- 
ion to  receive  the 
shock  of  the  explo- 
sion. The  straight 
eudiometer,  how- 
ever, is  cheaper,  and 
with  a  few  addi- 
tional attachments 
may  be  used  satis- 
factorily. A  in  the 
figure  is  an  open-top 
bell  jar,  such  as  has 
been  used  in  other 
experiments.  The 
neck  of  A  is  closed  with  a  tight-fitting,  1-hole  rubber 
stopper,  through  which  passes  a  glass  tube  having  an  en- 
largement blown  upon  the  lower  end,  at  B.  Another 
rubber  cork,  which  must  fit  the  eudiometer,  E,  very  tightly, 
is  put  upon  the  glass  tube  as  shown  in  the  figure.  This 
must  also  fit  very  tightly.  T  is  simply  a  piece  of  glass 
tubing  about  one  inch  in  diameter,  which  should  have  a 
capacity  somewhat  greater  than  E,  It  15  closed  at  the 


FIG.  H4. 


400  MODERN   CHEMISTRY 

lower  end  with  a  cork,  through  which  passes  a  short  glass 
tube.  A  rubber  tube  connects  the  two  portions  of  the 
apparatus,  and  just  above  B  is  fastened  by  some  fine  insu- 
lated copper  wire  wrapped  about  it. 

For  use  the  eudiometer  is  filled  with  water  and  sup- 
ported in  position  over  A.  The  gases  to  be  exploded  are 
introduced  separately,  and  each  measured  carefully,  the 
eudiometer  being  held  by  a  paper  test-tube  holder  at  such 
height  that  the  water  stands  at  the  same  level  inside  and 
outside.  Now  press  JB  firmly  down  upon  its  cork,  and 
lower  T  as  much  as  possible  in  order  that  the  confined 
gases  may  have  the  pressure  upon  them  reduced ;  grasp 
the  rubber  tubing  near  B  firmly  with  the  thumb  and 
finger,  and  pass  the  spark.  After  the  explosion,  adjust 
the  level  inside  and  outside  of  E  as  when  the  gases  were 
introduced,  and  measure  the  residue.  If  this  adjustment 
cannot  be  secured  by  lowering  E^  it  may  remain  connected 
as  when  the  spark  was  passed,  and  the  level  secured  by 
changing  the  height  of  T. 

20.  Aspirators  and  Aspirating  Bottles.  —  As  an  aid  in 
filtering  certain  classes  of  precipitates,  an  aspirator  is  fre- 
quently used.  This  acts  upon  the  principle 
of  the  Sprengel  air-pump.  The  aspirator  con- 
sists merely  of  two  tubes,  A  and  B,  secured 
at  right  angles  to  each  other.  A  is  attached 
to  a  water  faucet,  and  B,  by  means  of  heavy- 
walled  rubber  tubing,  to  a  filter  flask.  As 
FIG.  85.  ^ne  water  flows  through  A,  the  air  is  gradu- 
ally withdrawn  from  the  flask ;  the  pressure  being  thus 
removed  from  beneath  the  filter  containing  the  precipitate, 
the  liquid  is  forced  through  much  more  rapidly. 

The  filter  flask  is  usually  shaped  like  an  Erlenmeyer 
flask  (see  Fig.  86),  and  has  a  side  tube  for  connecting 


APPENDIX  F 


FIG.  87. 


FIG.  86. 


with  the  aspirator  at  B.  It  is  made  of  heavy  glass  so 
as  to  withstand  any  ordinary  atmospheric  pressure. 
For  use  it  is  fitted  with  a  rubber 
stopper  having  one  hole,  through 
which  the  stem  of  a  funnel  is  inserted. 
In  the  apex  of  the  funnel  is 
placed  a  small  platinum  cone, 
perforated  with  minute  open- 
ings. This  cone  is  used  to 
prevent  the  breaking  of  the 
filter  paper  by  the  atmospheric  pres- 
sure ;  at  the  same  time  the  numerous 
small  holes  permit  the  outflow  of  the 
filtrate  with  comparative  freedom. 

For  certain  experiments  an  aspirat- 
ing bottle  is  almost  indispensable.  For  example,  suppose 
the  experimenter  desires  to  cause  a  regular  flow  of  air  or 
of  some  other  gas  through  some  vessel,  suitable  apparatus 
is  necessary  and  may  be  very  easily  made.  Large  bottles, 

holding  3  or  4  liters, 
will  serve  best.  To 
each  fit  a  cork  with 
two  holes,  and  insert 
glass  tubing  as  shown 
in  the  accompanying 
figure.  The  bent 
tube,  6r,  has  attached 
a  short  piece  of  flex- 
ible rubber  tubing, 
upon  which  is  placed 
a  screw  clamp,  at  H. 
By  means  of  this  the 
FIG.S&  flow  of  gas  issuing 


402  MODERN  CHEMISTRY 

from  N  is  regulated.  The  bottle,  M,  is  placed  upon  a 
box  so  as  to  elevate  it  considerably  above  N.  A  rubber 
tube,  E,  connects  the  two  bottles,  and,  being  flexible, 
allows  of  the  elevation  of  either  bottle  above  the  other. 

If  you  desire  to  fill  N  with  any  gas  not  soluble  in  water, 
place  both  down  upon  the  table,  and  fill  N  completely 
with  water.  Open  the  clamp  at  H,  and  insert  the  cork 
with  the  tubing  into  N.  The  water  will  be  forced  out 
into  (7,  and  expel  the  air  therefrom  ;  this  done,  connect 
at  H  with  the  generating  flask  (not  shown  in  the  figure), 
after  having  waited  until  all  air  has  been  expelled  from  it. 
By  the  gas  pressure,  the  water  will  be  forced  from  N  over 
into  MI  continue  until  N  is  nearly  filled,  close  the  clamp 
at  H  tightly,  and  remove  the  generator.  Elevate  M  to  its 
position  upon  the  box,  and  the  aspirator  is  ready  for  use. 

By  simply  opening  the  screw  clamp,  the  siphon  connect- 
ing the  two  bottles  transfers  the  water  from  M  to  N  as 
rapidly  as  the  exit  of  gas  at  H  will  allow.  If  the  gas  has 
been  permitted  to  fill  completely  the  bottle  JV,  and  has 
forced  the  water  out  of  the  siphon  tube,  it  is  only  neces- 
sary to  apply  a  little  pressure  at  D.  If  a  dry  gas  is  de- 
sired, it  must  be  obtained  by  passage  from  N  through 
some  suitable  drying  tube  attached  at  H.  If  the  gas  to 
be  used  is  ordinary  air,  the  action  of  this  apparatus  may 
be  made  continuous,  except  for  a  momentary  delay  in 
changing  the  connections,  by  placing  first  M,  and  then  jV, 
upon  the  box,  and  connecting  the  receiver  with  the  tubes, 
G-  and  D,  respectively. 

The  apparatus  may  be  used  in  this  way  for  showing  the 
presence  of  carbon  dioxide  in  air,  by  forcing  it  through 
lime-water.  In  other  cases,  where  the  amount  of  gas 
needed  is  not  in  excess  of  the  capacity  of  the  bottle  JV", 
this  apparatus  will  work  with  entire  satisfaction. 


APPENDIX  F 


403 


21.  Gas  Generators.  —  It  is  often  desirable  to  have  a 
generator,  automatic  in  action,  which  will  furnish  a  steady 
flow  of  gas  and  be  ready  for  use  at  a  moment's  notice. 
Kipp's  apparatus  meets  such  a  demand ;  but  at  much  less 
expense  one  which  works  equally  well  may  be  prepared 
for  any  laboratory.  In  the  fig- 
ure, A  is  a  bottle  of  about  500  cc. 
capacity,  fitted  with  a  cork  and 
tube  at  P,  to  keep  out  dust. 
Through  the  bottom  at  K,  with 
a  glass  drill,  make  a  hole  and 
insert  a  rubber  cork  with  one 
perforation. 

Through  B  near  the  bottom 
drill  a  hole  and  insert  a  rubber 
cork  with  a  glass  tube  and  short 
rubber  connection  clamped  with 
a  Hoffman  screw.  This  is  for 
the  purpose  of  drawing  off  the 
spent  acid.  In  the  top  of  B  fit  a 
stopper  with  two  holes ;  through 
one  of  these  pass  a  long  tube 
reaching  to  the  bottom  of  B  and 
extending  up  into  A.  To  the  other  hole  fit  the  bent  tube, 
Z>,  which  has  rubber  connections  for  joining  with  any 
other  apparatus.  When  not  in  use,  this  is  kept  *tightly 
closed  with  a  screw  clamp. 

If  you  desire  to  use  this  apparatus  as  a  hydrogen  gener- 
ator, place  a  half  pound  or  more  of  zinc  in  B,  close  tightly 
the  screw  clamp  at  D,  and  pour  diluted  sulphuric  or  hydro- 
chloric acid  into  A  until  about  two- thirds  full.  Open  the 
screw  clamp ;  the  acid  will  run  down  into  the  lower  bottle 
and  will  continue  to  react  with  the  zinc  as  long  as  the  ga§ 


FIG.  89. 


404  MODERN  CHEMISTRY 

has  free  exit  at  D.  If,  however,  the  clamp  is  closed,  the 
pressure  in  B  soon  becomes  sufficient  to  force  the  acid  up 
the  longer  tube  into  the  upper  bottle,  and  the  evolution 
of  gas  ceases. 

Ci 

The  bottle,  A,  is  held  in  position  by  a  clamp  at  the  neck, 
and  rests  upon  a  ring  of  the  support.  The  holes  at  K  and 
E  may  be  drilled  by  using  a  large  file  broken  off,  together 
with  emery  dust.  To  use  the  generator  for  hydrogen 
sulphide  or  carbon  dioxide,  the  zinc  would  be  replaced 
with  ferrous  sulphide  or  marble. 

22.  Correction  of  Barometric  Reading.  —  In  the  various 
problems  given  in  the  text  in  connection  with  the  Law  of 
Charles,  it  was  assumed  without  being  stated  that  we  were 
dealing  with  dry  gases.  Further  than  this,  in  the  quanti- 
tative work  with  gases,  certain  corrections  have  been  neg- 
lected. For  exact  work,  however,  in  the  measurement  of 
gases,  not  only  must  the  temperature  be  known,  and  the 
barometric  pressure  as  well,  but  also  certain  other  facts. 
If  the  gas  has  been  collected  over  water,  the  exact  volume 
will  not  be  obtained  .by  methods  already  used,  for  the 
reason  that  the  presence  of  water  vapor  increases  the 
tension  of  the  gas,  and  hence  the  volume.  In  reducing 
the  volume  of  gases,  therefore,  to  standard  conditions, 
allowance  must  be  made  for  this  tension.  This  has  been 
carefully  estimated,  and  for  the  ordinary  range  of  tempera- 
ture is  shown  below  :  — 

19°  C.  .  .  16.35mm.  22.0°  C.  .  .  19.66mm. 

19.5°  C.  .  .  16.86    "  22.5°  C.  .  .  20.27    " 

20.0°  C.  .  .  17.39    "  23.0°  C.  .  .  20.89    " 

20.5°  C.  .  .  17.94    "  23.5°  C.  .  .  21.53    " 

21.0°  C.  .  .  18.50    "  24.0°  C.  .  .  22.18    " 

21,5°  C.  ,  19.07    "  24.5°  C.  .  22.86    " 


APPENDIX  F  405 

To  illustrate,  suppose  we  have  40  cc.  of  gas,  the  tern- 
perature  of  the  room  being  21°  C.,  the  barometric  pressure 
740.  According  to  the  law,  stated  previously,  — 

V.  V  :.P'  :P, 

V  X  P' 


or 


in  which  V  represents  volume  under  standard  pressure  P, 
which  is  760,  V1  the  given  volume  of  gas  under  the  pres- 
sure P'.  Substituting,  — 

rr=40  x  740 

760 

But  making  correction  for  aqueous  tension,  we  have 

v_  F'xQP'  -p) 
P 

in  which  p  is  the  tension  of  the  aqueous  vapor.  From  the 
table  given  above,  we  find  that  at  21°  C.  this  is  18.5  mm. 
Substituting  in  the  formula,  we  have,  — 

F=40  x  (740 -18.5) 
760 

which  will  give  the  true  volume  of  the  gas  under  standard 
conditions. 

23.  Drying  Tubes.  —  Drying  may  usually  be  accom- 
plished by  forcing  a  strong  current  of  air  through  the 
tube  by  means  of  a  foot-bellows ;  if  the  tube  has  been 
previously  moistened  with  alcohol,  the  process  will  be 
materially  hastened.  In  like  manner  flasks  may  be  dried. 
By  means  of  rubber  tubing  connect  a  glass  tube,  long 
enough  to  reach  to  the  bottom  of  the  flask,  to  a  foot-bel- 
lows, and  direct  a  strong  current  of  air  into  the  fla,ski 


406  MODERN  CHEMISTRY 

24.  Recording  Results  of  Experiments.  —  In   the  first 
place,  the  student  should  understand  exactly  what  he  is 
expected  to  learn  from  the  experiment ;    then   he   must 
know  what  steps   are   necessary   in   order  to   secure   the 
correct  results.      Do  not  make  the  mistake  of  drawing 
conclusions  before  the  experiment  is  complete,  and  then 
endeavoring  to  make  the  results  conform  to  your  precon- 
ceived ideas.     Learn  to  see  everything  that  occurs,  and 
draw  your  conclusions  in   accordance   with  what   really 
happens. 

These  results  should  be  recorded  in  suitable  note-books, 
and,  were  it  possible,  always  completed  in  the  laboratory. 
Note  the  results  neatly  and  concisely  in  good  rhetorical 
sentences.  When  they  admit  of  being  tabulated,  such  a 
form  is  always  desirable.  If  the  notes  are  not  written  up 
in  the  laboratory,  a  brief  record  should  be  made  th  re, 
and  at  home  put  into  permanent  form  in  the  note-book 
without  delay.  These  records  should  be  examined  fre- 
quently by  the  teacher,  at  least  after  the  completion  of 
each  distinctive  portion  of  the  work ;  for  instance,  in 
studying  the  halogen  group,  when  the  work  in  chlorine 
has  been  done,  the  notes  should  be  examined ;  after  that 
in  bromine  is  completed,  a  similar  examination  should 

take  place. 

PREPARING  SOLUTIONS 

25.  For  ordinary  work,  reagents  which  are  "  commer- 
cially pure"  will  do,  and  are  much  cheaper.     It  is  better 
to  use  distilled  water  in  making  up  all  solutions,  but  for 
some,  such  as  caustic  potash,  soda,  and  such  as  form  pre- 
cipitates with  water  that  is  more  or  less  "hard,"  pure 
water  is  essential. 

26.  Acids  —  Hydrochloric,  Nitric,  and  Sulphuric.  —  For 
ordinary  work  these  acids  should  be  diluted  with  twice/ 


APPENDIX  F  407 

their  own  volume  of  water.  In  the  case  of  the  last  acid 
the  water  must  be  added  very  cautiously,  as  great  heat  is 
generated.  It  is  better  to  take  what  water  is  to  be  used 
in  diluting  the  acid,  and  very  gradually  add  the  sulphuric 
acid  to  it.  Acetic  acid  may  also  be  diluted.  When  an 
acid  stronger  than  the  one  prepared  in  this  way  is  de- 
manded, it  is  so  stated  in  the  text. 

27.  Ammonia.  —  Ordinary   aqua   ammonia    should    be 
diluted  with  about  three  parts  of  water. 

28.  Ammonium   Chloride. — This   should  be   made   up 
with  about  100  g.  of  the  salt  to  a  liter  of  water. 

29.  Ammonium  Carbonate.  —  About  200  g.  to  liter. 

30.  Ammonium  Oxalate.  —  About  40  g.  to  liter. 

31.  Ammonium  Sulphide.  —  This  may  be  prepared  by 
the  teacher  if  preferred.     It  is  done  by  taking  ammonium 
hydroxide  as  diluted  above  and  passing  into  it  a  current 
of  hydrogen  sulphide  until  saturated.     If  yellow  ammo- 
nium sulphide,  (NH4)2SX,  is  desired,  add  to  the  ammonia 
at  the  beginning  a  little  sulphur  in  the  form  of  flowers. 
When  the  solution  is  saturated,  it  is  customary  to  add 
to  it  about  two-thirds  as  much  more  of  the  ammonium 
hydroxide. 

32.  Barium  Chloride.  — About  100  g.  to  the  liter. 

33.  Potassium  Dichromate.  —About  50  g.  to  the  liter. 

34.  Potassium    Ferrocyanide.  —  About    75   g.    to   the 
liter. 

35.  Calcium  Hydroxide.  — Saturated  solution. 

36.  Mercuric  Chloride.  —  Saturated  solution. 

37.  Mercurous  Nitrate.  — About  50  g.  to  the  liter,  witft 
about  one-twentieth  part  of  nitric  acid  added.     Otherwise 
a  basic  salt  forms  in  the  solution.     It  is  a  very  good  plan 
to  put  a  few  drops  of  mercury  into  the  bottle  containing 
the  solution. 


408  MODERN  CHEMISTRY 

38.  Silver  Nitrate.  —  About  50  g.  to  the  liter.     Keep 
the  solution  in  an   amber-colored  bottle  and  away  from 
contact  with  organic  substances. 

39.  Ferric  Chloride.  —  About  50  g.  to  the  liter. 

40.  Ferrous   Sulphate.  —  This    must    be    made    up    as 
desired.     About  100  g.  to  the  liter. 

41.  Lead  Acetate.  —  About  100  g.  to  the  liter. 

42.  Potassium  Iodide.  —  About  50  g.  to  the  liter. 

OTHER  SOLUTIONS  USED  OCCASIONALLY 

43.  Arsenic  Chloride.  —  Dissolve  arsenious  oxide,  As2O3, 
in  caustic  soda,  and  then  add  hydrochloric  acid  until  the 
solution  gives  an  acid  reaction. 

44.  Antimony   Chloride. — Add    hydrochloric    acid    to 
^water  until  well  acidulated,  and  then  a  small  quantity  of 
antimony   trichloride ;    a   solution   of   antimony   may   be 
obtained  from  the  antimony  tartrate  in  the  same  way. 

45.  Bismuth  Nitrate.  —  This  must  be  prepared  in  the 
same  manner  as  the  antimony  chloride.     Dissolve  a  few 
crystals  of  the  salt  in  water  to  which  considerable  nitric 
acid  has  been  added. 

46.  Calcium  Chloride.  —  About  100  g.  to  the  liter. 

47.  Calcium  Sulphate.  —  Saturated  solution. 

48.  Cobalt  Nitrate.  —  About  50  g.  to  liter. 

49.  Chromium  Chloride.  —  Prepare  as  indicated  in  the 
text.     To  a  solution  of  potassium  dichromate  add  about 
one-twentieth    as    much   hydrochloric    acid   and   a   little 
alcohol,  and  boil.     The  green  solution  obtained  will  be 
chromium  chloride. 

50.  Copper  Sulphate.  —  About  50  g.  to  liter. 

51.  Di-sodium  Phosphate.  — About  100  g.  to  liter. 

52.  Potassium  Cyanide.  —  About  100  g.  to  liter. 

53.  Potassium  Chromate.  —  About  50  g.  to  liter. 


APPENDIX  F 


409 


54    Potassium  Hydroxide.  —  About  100  g.  to  liter. 

55.  Sodium  Hydroxide.  — About  100  g.  to  liter. 

56.  Magnesium  Sulphate.  —  About  100  g.  to  liter. 

57.  Sodium  Carbonate.  —  About  100  g.  to  liter. 

58.  Lead  Nitrate.  — About  100  g.  to  liter. 

59.  Stannous  Chloride.  —  First  add  about  one-twentieth 
part  of  hydrochloric  acid  to  the  water,  and  then  about 
75  g.  of  the  solid  to  a  liter.     It  is  better  to  put  a  piece  of 
granulated  tin  into  the  solution. 

60.  Cochineal  Solution.  —  Grind  up  the  solid  in  a  mortar 
and  dissolve  in  water  or  in  a.10  per  cent  solution  of  alcohol. 

61.  Indigo  Solution.  — Treat  about  1  g.  of  indigo  with 
about  10  g.  of  sulphuric  acid.     After  standing  several 
days,  dissolve  the  whole  in  water. 

62 .  Litmus  Solution. — Dissolve  the  blue  solid,  powdered, 
in  water. 

63.  Phenol -phthalein.  —  Dissolve  about  1  g.  in  100  cc. 
of  50  per  cent  alcohol. 

64.  Ammonium  Molybdate.  —  Dissolve   15    g.    of    am- 
monium molybdate  crystals  in  100  cc.  of  aqua  ammonia 
as   prepared   above.     To   this   add  an  equal   volume   of 
distilled  water,  and  finally  125  cc.  of  nitric  acid,  specific 
gravity  about  1.4. 

SUPPLIES  NEEDED. 


65.    Chemicals.  — For  ten  students. 


Acid,  Acetic 1  Ib. 

"     Hydrochloric     ....  10 

"     Nitric 6 

"     Oxalic k 

Sulphuric 10 

"     Tartaric i 

Alcohol 1  qt. 

Alum 1  Ib. 

Aluminum 2  oz. 

Ammonium  Carbonate    ...  1  Ib. 

"           Chloride  ....  1  Ib. 


Ammonium  Ferric  Citrate 

"  Hydroxide  . 

"  Nitrate    .    . 

"  Sulphate 

"  Sulphide 

Antimony,  Metallic    .    . 

"         Potassium  Tartrate 
Trichloride   .     .    . 

Arsenic,  Metallic 

Arsenic,  Trioxide 

Barium  Chloride 


loz. 

81b. 


* 

loz. 
Jib. 
i  Ib. 


410 


MODERN  CSEMISTRT 


*'        Nitrate 

«' 

Mercurous  Nitrate 

V   ^"« 

i  " 

Bark  Charcoal 

(( 

Nickel              " 

i  " 

Bismuth  Metallic  .     :     .     .     . 

(( 

1  OZ. 

"         Nitrate    

« 

Paraffin      

4    " 

Bleaching  Powder  

« 

Phenolphthalein      .... 

1  OZ 

Bromine              

2  OZ. 

Platinum  Wire  

3ft. 

Calcium  Carbide     

3    lb. 

Phosphorus,  Ordinary 

"        Chloride             .     . 

4    " 

Plaster  of  Paris  

3    " 

"        Fluoride 

4    " 

Potassium  Hydroxide  sticks  '  . 

1    " 

"        Sulphate 

4    " 

Iodide  

2    " 

Carbon  Bisulphide      .... 
Charcoal,  Powdered,  animal   . 
"         Stick 

4     " 

4  " 
1  doz. 

Bromide   .... 
Carbonate     .     .     . 
Chlorate  .... 

l    (( 

I    " 
1    " 

"         Wood,  powdered      . 
Cobalt  Nitrate 

Jib. 

i  " 

Chromate     .    .    . 
Cyanide                 . 

4    " 
1    " 

1      " 

Dichromate 

5    " 

Copper,  Metallic,  turnings  .     . 
"        Nitrate 

2  " 

i  « 

Ferrocyanide    .     . 
Ferricyanide 

1      (C 

"        Oxide    

I  " 

Metallic    .... 

A  " 

"        Sulphate    

4    " 

Nitrate     .... 

3    " 

Ether              

J      ' 

Nitrite     .... 

k   " 

Permanganate  . 

i    (« 

1      < 

Sulphocyanide  .     . 

i   " 

IS      ' 

Shellac  

1  OZ. 

IS      ' 

Silver  Nitrate     

i  lb. 

3      < 

"    Filings 

l      < 

Tetraborate  (Borax)  . 

4  " 

"    Sulphate 

Carbonate     .... 

1  " 

"    Sulphide 

2    ' 

Chloride    

1  " 

"    Wire  

i    ( 

Hydroxide,  sticks 

1  " 

£    ' 

Nitrate      .    .     .    . 

1  " 

"      Metallic 

Nitrite  

5    " 

"      Nitrate      

i    < 

Phosphate,  Di    .    .    . 

5    " 

i    < 

Sulphide  

5    " 

»    ' 

Sulphite    

1     " 

1    ' 

Thiosulphate     .     .     . 

3    " 

Starch    

k    " 

10 

Strontium  Nitrate  

1    n 

Sucrar 

1    " 

1  OZ. 

1    " 

"         roll       .         .... 

1    " 

"          Powdered 

4     " 

Tin  Metallic  

3    " 

u          Sulphate 

1     <' 

"    Chloride      

i    " 

Manganese  Chloride   .... 
"          Dioxide 

4     " 
1     " 

"    Tetrachloride       .... 
Turpentine     

1  OZ. 

1  lb. 

Marble 

2  " 

Zinc,  Granulated    

2  " 

»   " 

"     Dust      .         .          ... 

i   " 

"     Sheet              

1  " 

.     *^  t 

4    " 

4  " 

Oxide  . 

4  " 

APPENDIX  G 

REFERENCE  LIBRARY 

No  text  on  chemistry  can  hope  to  give  more  than  a 
glimpse  at  the  subject.  Naturally,  therefore,  it  should 
be  the  aim  of  every  teacher  to  build  up  a  reference  library 
for  the  use  of  himself  and  students.  Among  the  many 
good  books  to  be  obtained,  the  following  are  suggested  :  — 

Newth's  Inorganic  Chemistry  —  Longmans. 

Newth's  Chemical  Lecture  Experiments  —  Longmans. 

Mendeleeff's  Principles  of  Chemistry  —  Longmans. 

OstwalcTs  Outlines  of  General  Chemistry  —  Macmillan. 

Ostwalds  Foundations  of  Analytical   Chemistry  —  Mac- 
millan. 

Walker- Dobbin1  s  Chemical  Theory  for  Beginners  —  Mac- 
millan. 

Roscoe  and  Schorlemmer' s  Treatise  on  Chemistry,  Vols.  I 
and  II  —  Apple  ton. 

Remsen's  Chemistry,  Advanced  Course  —  Holt. 

Remssn's  Theoretical  Chemistry  —  Lee. 

Ramsay's   Experimental   Proofs   of    Chemical  Theory  — 
Macmillan. 

Cornishes  Practical  Proofs  of  Chemical  Laws  —  Longmans. 

Johnston's  Chemistry  of  Common  Life  —  Appleton. 

Lassar-Cohn's  Chemistry  of  Every-day  Life  —  Lippiucott. 

Ramsay's  Gases  of  the  Atmosphere  —  Macmillan. 

Meyer's  History  of  Chemistry  —  Macmillan. 

Thorpe's  Essays  in  Historical  Chemistry  —  Macmillan. 

,411 


412  MODERN  CHEMISTBT 

Sutton's  Volumetric  Analysis  —  Blakiston. 

Addymaris  Agricultural  Analysis  —  Longmans. 

Alembic  Club  Reprints  —  Chemical  Pub.  Co.,  Easton,  Pa. 

Foundations  of  the  Atomic  Theory. 

Experiments  on  Air. 

Foundations  of  the  Molecular  Theory. 

Discovery  of  Oxygen. 

Elementary  Nature  of  Chlorine. 

Liquefaction  of  Gases. 

Early  History  of  Chlorine. 
Muirs  Heroes  of  Science  —  Young  &  Co. 
Shenstone's  Glass  Blowing  —  Longmans. 
Thorpe 's  Chemical  Preparations  —  Ginn. 


APPENDIX  H 

BIOGRAPHICAL 

THE  following  are  among  those  who  have  contributed  to 
chemical  literature  or  to  the  advancement  of  the  science. 

AGE  OF  ALCHEMY 

G-eber.  —  Arabian  alchemist  of  eighth  century ;  author 
of  several  chemical  works,  and  discoverer  of  aqua  regia. 

Albertus  Magnus.  —  Died  1280.  Advanced  the  theory 
that  the  metals  were  composed  of  water,  arsenic,  and 
sulphur. 

Bacon,  Roger.  —  Thirteenth  century.  English  alche- 
mist. Advocated  experimental  proof  of  chemical  theory. 
Inventor  of  gunpowder. 

Valentine,  Basil.  —  Fifteenth  century.  Wrote  several 
works  on  chemistry.  Probably  a  fictitious  name  of 
Johann  Tholde. 


APPENDIX  H  413 

MEDICAL  ERA  OF  CHEMISTRY 

Paracelsus,  a  name  coined  for  himself  by  Theophrastus 
Bombastus  von  Hohenheim.  —  Early  part  of  the  sixteenth 
century.  By  his  study  and  preparation  of  a  large  number 
of  medicines,  he  earned  for  himself  the  title,  "  Father  of 
Medicine." 

Libavius.  —  Died  in  1616.  Proceeded  with  the  work 
begun  by  Paracelsus.  Wrote  a  Handbook  of  Chemistry. 

Van  Helmont,  Jean  Baptiste.  — 1577—1644.  Discov- 
ered several  gases. 

Boyle,  Robert.  —  1627-1691.  Real  founder  of  the 
sciences  of  physics  and  chemistry.  Formulated  Boyle's 
Law,  and  advanced  the  true  theory  as  to  the  composi- 
tion of  matter. 

Becker,  Johann  Joachim.  — 1635-1682.  German  chem- 
ist. Author  of  theory  that  when  a  metal  burns  terra 
pinguis  escapes  from  it. 

AGE  OF  PHLOGISTON 

Stahl,  G-eorg  Ernst.  — 1660-1734.  Founder  of  the  phlo- 
gistic theory  of  combustion,  that  all  combustible  sub- 
stances contained  an  unknown  something  called  phlogiston 
which  escaped  when  the  substance  burned.  It  was  an 
outgrowth  of  Becher's  theory. 

Hoffmann,  Christoph  Ludwig.  — 1721-1807.  Physicist 
and  chemist.  His  theory  of  the  reduction  of  a  metal  was 
about  the  same  as  that  held  to-day.  He  believed  that 
the  calces  of  the  metals  contained  the  metals  themselves 
and  some  other  substance,  which  he  called  sal  acidum. 

Black,  Joseph.  — 1728-1799.  Professor  of  chemistry  in 
Edinburgh.  Discovered  carbon  dioxide  arid  proved  that 


414  MODERN  CHEMISTRY 

the  carbonates  of  the  alkalies  and  alkaline  earths  are 
not  elements. 

Cavendish,  Henry.  — 1731-1810.  Discovered  hydrogen  ; 
studied  the  composition  of  water  and  the  air,  and  made 
a  large  number  of  experiments  with  the  latter.  Prepared 
nitric  acid  by  synthesis. 

Priestley,  Joseph.  — 1733-1804.  Discoverer  of  oxygen, 
and  strong  advocate  of  phlogistic  theory. 

Scheele,  Carl  Wilhelm.  -- 1742-1786.  Discoverer  of 
chlorine;  made  some  investigations  in  organic  chemistry; 
prepared  glycerine  and  prussic  acid. 

MODERN  ERA  OF  CHEMISTRY 

This  coincides  roughly  with  the  nineteenth  century. 

Lavoisier,  Antoine  Laurent. — 1743—1794.  Founder  of 
modern  chemistry.  Made  a  beginning  in  quantitative 
work,  and  overthrew  the  theory  of  phlogiston.  Advanced 
the  idea  of  the  conservation  of  matter. 

Gray-Lussac,  Joseph  Louis.  —  1778-1850.  Author  of 
the  law  of  combination  of  gases  by  volume.  Made  an 
extensive  study  of  the  general  properties  of  gases ;  deter- 
mined the  relation  between  the  volume  of  a  gas  and  its 
temperature,  thus  supplementing  Boyle's  work. 

Berzelius,  Johann  Jacob,  Baron.  —  1779-1848.  Studied 
the  atomic  weights  of  the  elements ;  improved  the  usual 
methods  of  chemical  analysis,  and  investigated  the  law 
of  combining  proportions. 

Proust,  Louis  Joseph.— 1760-1826.  Advocated  the  theory 
that  the  elements  combine  always  in  definite  proportions, 
now  known  as  the  "Law  of  Definite  Proportions." 

Dalton,  John.  —  1766-1844.  Advanced  the  atomic 
theory  of  matter,  and  formulated  the  "  Law  of  Multiple 
Proportions." 


APPENDIX  H  415 

BertMlet,  Claude  Louis. — 1748-1822.  Made  a  long 
series  of  experiments,  studying  the  behavior  of  ammonia, 
hydrogen  sulphide,  chlorine,  and  other  gases. 

Davy,  Sir  Humphry.  —1778-1829.  Studied  the  prop- 
erties of  various  gases ;  proved  that  the  alkalies,  caustic 
soda  and  potash,  are  not  elements. 

Dulong  and  Petit.  —  Early  part  of  nineteenth  century. 
Made  a  study  of  the  metals.  Formulated  the  law  that 
the  specific  heats  of  the  metals  are  inversely  proportional 
to  their  atomic  weights. 

Dumas,  Jean  Baptiste  Andre.  —  1800-1884.  Made  an 
extensive  study  of  vapor  densities. 

Faraday,  Michael.  — 1791-1867.  Succeeded  in  liquefy- 
ing many  of  the  gases;  studied  physical  chemistry,  and 
determined  the  effects  of  an  electric  current  upon  electro- 
lytes. He  formulated  the  "  Law  of  Definite  Electrolytic 
Action,"  that  an  electric  current  decomposes  electrolytes 
so  that  equivalent  amounts  of  the  substance  are  liberated 
at  the  kathode  and  anode. 

LieUg,  Justus,  Freiherr  von.  — 1803-1873.  Studied 
organic  chemistry  ;  investigated  the  phenomenon  of 
isomerism. 

Mendeleeff,  Dmitri  Ivanovich.  —  Born  1834.  Russian 
chemist.  Formulated  the  "  Periodic  Law  of  the  Ele- 
ments." Author  of  general  chemistry. 

Pictet  and  Cailletet.  —  Physico-chemists  of  the  present 
time.  They  have  done  much  work  in  producing  low 
temperatures,  and  in  liquefying  air,  hydrogen,  and 
oxygen. 

Ramsay,  William.  —  Born  1852.  Discoverer  of  argon 
in  1894.  English  scientist  of  to-day. 

Dewar,  James.  —  Born  1842.  English  scientist  of  the 
present  time.  Has  studied  carefully  low  temperatures, 


416  MODERN  CHEMISTRY 

Moissan,  Henry.  —  French  chemist  of  the  present  time. 
Has  succeeded  in  preparing  artificial  diamonds ;  has 
also  studied  carefully  the  properties  of  liquid  fluorine. 

MEANING  OF  ALCHEMISTIC  TERMS 

The  student  in  attempting  to  read  the  reports  of  the  chemists  of 
the  eighteenth  century  will  find  much  difficulty  in  understanding  the 
alchernistic  terms  so  universally  employed.  The  following  are  among 
those  most  commonly  met  with,  and  are  given  to  encourage  the  student 
to  read  these  accounts  himself.  The  Alembic  Club  Reprints,  men- 
tioned among  the  books  suitable  for  reference,  furnish  the  most 
desirable  portions  of  the  writings  of  such  investigators  as  Scheele, 
Dalton,  Priestley,  and  others.  It  will  be  noticed  that  often  several 
terms  are  used  for  the  same  substance.  This  was  in  accordance  with 
the  plans  of  alchemy  to  keep  secret  the  discoveries  and  mystify  any 
who  might  attempt  to  decipher  the  records. 

OLD  TERMS  PRESENT  MEANING 

Acid   .....  Anhydride  (oxide). 

Acid  of  chalk      .         .         .  Carbon  dioxide. 

Acidum  salis       .         .        .  Hydrochloric  acid 

Aer  fixus     ....  Carbon  dioxide. 

Air Gas. 

Alkali  of  tartar  .         .         .  Potassium  carbonate. 

Aqua  fortis          .        .         .  Nitric  acid. 

Aqua  regis  ....  Aqua  regia. 

Azotic  gas  ....  Nitrogen. 

Blanc  d'Espagne         .        .  Bismuth  Subnitrate. 

Calx Oxide. 

Calx  of  silver      .         .        .  Silver  oxide. 

Colcothar    ....  Ferric  oxide. 

Dephlogisticated  air   .         .  Oxygen. 

Draco  mitigatus          .        .  Mercurous  chloride. 

Fire  air  .         .        .  Oxygen. 

Fixed  air    .         .        .        .  Carbon  dioxide. 

Fixed  alkali        .         .         .  Sodium  carbonate. 

Gas  fuliginosurn         ,        .  Combustible  gas, 


APPENDIX  H 


417 


OLD  TERMS 

Gas  pingue 

Gas  siccum 

Gas  sylvestre 

Grey  calx  of  lead 

Hartshorn  . 

Liver  of  Sulphur 

Magnesia  alba     . 

Marcasite    . 

Marine  acid        .         .         . 

Mephitic  air 

Mercurius  calcinatus  . 

Mercurius  dulcis 

Mercurius  Niter 

Mercurius  precipitatus  per 

se 

Mercurius  precipitatus 

ruber       .... 
Mercurius  sublimatus 
Mercurius  vitae  . 
Mors  metallorum 

Niter 

Nitrous  air 
Nitrous  gas 
Phlogiston  .... 


Phlogistic  air 
Pulvis  angelicus . 
Spirit  of  niter     . 
Spirit  of  sulphur 
Spiritus  igneo  aerius 
Spiritus  salis 
Terra  pinguis 
Usifur 
Vital  air     . 
Vitriol 

Vitriolated  tartar 
Volatile  alkali    . 


PRESENT  MEANING 

Combustible  gas. 
Combustible  gas. 
Carbon  dioxide. 
Lead  sesquioxide. 
Ammonia. 

Potassium  persulphide. 
Magnesium  carbonate. 
Ferric  sulphide. 
Hydrochloric  acid. 
Nitrogen. 
Mercuric  oxide. 
Mercurous  chloride. 
Mercuric  nitrate. 

Mercuric  oxide. 

Mercuric  oxide. 
Mercuric  chloride. 
Antimony  oxychloride. 
Mercuric  chloride. 
Potassium  nitrate. 
Nitrogen  dioxide. 
Nitrogen  dioxide. 
A  hypothetical  substance,  be 

lieved  to  exist  in  all  com 

bustible  bodies. 
Nitrogen. 

Antimony  oxychloride. 
Nitric  acid. 
Sulphuric  acid. 
Oxygen. 

Hydrochloric  acid. 
Same  meaning  as  phlogiston 
Artificial  mercuric  sulphide. 
Oxygen. 
Sulphate. 

Potassium  sulphate. 
Ammonium  Carbonate. 


418 


MODERN  CHEMISTRY 


TABLE  OF   THE  ELEMENTS  AND   THEIR 
ATOMIC   WEIGHTS 


NAME 


Aluminum Al 

Antimony Sb 

Argon A 

Arsenic As 

Barium Ba 

Bismuth Bi 

Boron B 

Bromine Br 

Cadmium Cd 

Caesium Cs 

Calcium .  Ca 

Carbon    .     . C 

Cerium Ce 

Chlorine Cl 

Chromium Cr 

Cobalt     ...     o     ....  Co 

Columbium Cb 

Copper Cu 

Erbium E 

Fluorine F 

Gadolinium Gd 

Gallium  . Ga 

Germanium Ge 

Glucinum Gl 

Gold Au 

Helium He 

Hydrogen H 

Indium In 

Iodine I 

Iridium Ir 

Iron Fe 

Krypton Kr 


SYMBOL 


ATOMIC  WEIGHTS 


O  =  16 


27.1 
120. 

39.9 

75. 
137.4 
208.5 

11. 

79.96 
112.4 
133. 

40. 

12. 
140. 

35.45 

52.1 

59. 

94. 

63.6 
166. 

19. 
156. 

70. 

72. 
9.1 
197.2 
4. 

1.01 
114. 
126.85 
193. 

56. 

81.8 


APPENDIX  H 


419 


TABLE  OF  THE  ELEMENTS  AND  THEIR  ATOMIC 
WEIGHTS—  Continued 


NAME 


SYMBOL 


ATOMIC  WEIGHTS 


H  = 


Lanthanum La 

Lead Pb 

Lithium Li 

Magnesium Mg 

Manganese Mn 

Mercury Hg 

Molybdenum Mo 

Neodymium Nd 

Neon Ne 

Nickel Ni 

Nitrogen      ...     =     ...  N 

Osmium Os 

Oxygen O 

Palladium Pd 

Phosphorus P 

Platinum Pt 

Potassium K 

Praseodymium Pr 

Rhodium Rh 

Rubidium Rb 

Ruthenium Ru 

Samarium Sm 

Scandium Sc 

Selenium Se 

Silicon Si 

Silver Ag 

Sodium Na 

Strontium Sr 

Sulphur S 

Tantalum Ta 

Tellurium Te 

Terbium  Tr 


138. 
206.9 
7. 

24.36 

55. 
200.3 

96. 
143.6 

20. 

58.7 

14.04 
191. 

16. 
106. 

31. 
194.8 

39.15 
140.5 
103. 

85.4 
101.7 
150. 

44.1 

79.1 

28.4 
107.93 

23.05 

87.6 

32.06 
183. 
127. 
160. 


137.6 

205.36 
6.97 
24.1 
54.6 

198.50 
95.3 

142.5 

9 

58.25 
13.93 
189.6 
15.88 
106.2 
30.75 
193.4 
38.82 
139.4 
102.2 
84.75 
100.9 
149.2 
43.8 
78.6 
28.2 
107.11 
22.88 
86.95 
31.83 
181.5 
126.5 
158.8 


420 


MODERN  CHEMISTRY 


TABLE  OF  THE  ELEMENTS   AND  THEIR  ATOMIC 
WEIGHTS—  Continued 


NAME 


SYMBOL 


ATOMIC  WEIGHTS 


O  =  16 


Thallium Tl 

Thorium Th 

Thulium Tm 

Tin Sn 

Titanium Ti 

Tungsten W 

Uranium U 

Vanadium V 

Xenon X 

Ytterbium  .......  Yb 

Yttrium Y 

Zinc Zn 

Zirconium Zr 


204.1 
232.5 
171. 
118.5 

48.1 
184. 
239.5 

51.2 
128. 
173. 

89. 

65.4 

90.7 


202.61 

230.8 

169:4 

118.1 

47.8 

182.6 

237.8 

51.0 

? 

171.9 
88.3 
64.9 
89.7 


The  above  table  shows  two  columns  of  atomic  weights;  the  first  as- 
sumes O  =  16  as  the  standard,  the  second,  H  =  1. 


GLOSSARY  OF  CHEMICALS  AND  MINERALS 

Agate.     A  variety  of  quartz,  occurring  often  in  variegated  colors, 

arranged  concentrically. 

alabaster.     A  fine-grained,  white  variety  of  gypsum, 
alum.    A  double  sulphate,  of  general  formula,  M2R2(SO4)4  24  HaO. 
alumina.     Aluminum  oxide,  A12O3. 
amethyst.     A  variety  of  quartz, 
anthracite.     Natural  coal,  possessing  little  or  no  oil  or  other  volatile : 

products.     Hard  coal. 

antichlor.     A  reagent  used  to  neutralize  chlorine  when  in  excess, 
aragonite.     A  variety  of  calcite,  CaCO3. 
argentite.     Native  silver  sulphide, 
arsenic.     The  popular  name  for  arsenic  trioxide. 
arsenious  acid.     Another  name  for  arsenic  trioxide. 
arsine.     Hydrogen  arsenide,  AsH3. 
azurite.     An  ore  of  copper,   blue  in  color,  composition  Cu(OH)2, 

2  CuCO3. 

Baryta.     Barium  oxide, 
baryta  water.     Barium  hydroxide, 
bauxite.     A  hydrated  oxide  of  aluminum,  A12O3,  H2O,  used  as  a  source 

for  aluminum. 

benzine.     A  light  oil  obtained  from  petroleum, 
bicarbonate  of  soda.     Cooking  soda,  NaHCO3. 
bismuth  ocher.     Bismuth  oxide,  Bi2O3. 
bismuthite.     Native  bismuth  sulphide. 

bituminous.     Containing  bitumen  or  oil.     Applied  to  soft  coals, 
blanc  de  fard.     Bismuth  subuitrate,  BiONO3. 
blende.     Native  zinc  sulphide, 
blue  vitriol.     Copper  sulphate, 
borax.     Sodium  tetraborate,  Na2B4O7. 
braunite.     Native  Mn2O3. 

butter  of  antimony.     An  old  name  for  antimony  trichloride. 
Calamine.     An  ore  of  zinc,  Zn2SiO4,  H2O. 

421 


422  MODERN  CHEMISTRY 

calchopyrite.     A  sulphide  of  iron  and  copper,  CuaS,  Fe2S3. 

calcite.     Crystallized  calcium  carbonate. 

calomel.     Mercurous  chloride,  Hg2Cl2. 

carbonado.  A  variety  of  diamond  occurring  in  black  pebbles  01 
masses. 

carborundum.  A  hard  substance,  made  by  combining,  at  high  tempera- 
tures, silica  and  carbon. 

cassiterite.     Native  stannic  oxide,  SnO2,  the  chief  ore  of  tin. 

caustic  potash.     Potassium  hydroxide. 

caustic  soda.     Sodium  hydroxide. 

celestite.     Strontium  sulphate. 

cement.  A  variety  of  lime  prepared  from  limestone  containing  from 
40  to  50  per  cent  of  slate. 

chalcedony.     A  variety  of  quartz. 

chalk.     A  soft  variety  of  limestone,  composed  of  the  shells  of  diatoms. 

chloride  of  lime.     A  common  name  for  bleaching  powder. 

chrome  alum.     A  sulphate  of  potassium  and  chromium. 

chrome  red.     Basic  lead  chromate,  Pb2CrO5. 

chrome  yellow.     Lead  chromate,  PbCrO4. 

cinnabar.     The  chief  ore  of  mercury,  HgS. 

clay.     A  hydrated  silicate  of  aluminum,  containing  various  impurities. 

colcothar.     Ferric  oxide,  Fe2O3. 

copperas.     Ferrous  sulphate. 

corrosive  sublimate.     Mercuric  chloride,  HgCl2. 

corundum.     Anhydrous  alumina,  uncrystallized. 

cryolite.     A  fluoride  of  sodium  and  aluminum,  NaAlF4. 

Dolomite.     A  native  carbonate  of  magnesium  and  calcium. 

Emerald.     (Oriental.)     Crystallized  alumina,  green  in  color. 

emery.     Massive,  opaque  alumina. 

epsom  salts.     Magnesium  sulphate. 

euchlorine.     A  solution  of  chlorine  in  water. 

Fat  lime.     Lime  made  from  pure  limestone. 

feldspar.  A  silicate  of  potassium  and  aluminum,  which,  decomposed, 
forms  clay. 

fool's  gold.     Ferric  disulphide,  FeS2. 

fuller's  earth.     A  variety  of  clay. 

fuming  liquor  of  Libavius.     Anhydrous  stannic  chloride. 

Galena.     The  chief  ore  of  lead,  PbS. 

green  vitriol.    Ferrous  sulphate. 


GLOSSARY  423 

gypsum.     Native  calcium  sulphate. 

Hartshorn.     An  old  term  for  ammonia. 

heavy  spar.     Native  barium  sulphate. 

hematite.     An  important  ore  of  iron,  of  the  composition  FegOg. 

horn  silver.     Native  silver  chloride. 

hydraulic  cement.  Lime  containing  from  10  to  30  per  cent  of  silica, 
having  the  property  of  hardening  under  water. 

hypo.     The  photographer's  name  for  sodium  thiosulphate. 

Iceland  spar.     A  transparent,  crystalline  variety  of  calcium  carbonate. 

infusorial  earth.  A  grayish  white  earth,  composed  largely  of  silica, 
resulting  from  the  secretion  of  diatoms. 

Jeweler's  rouge.  An  oxide  of  iron,  red  in  color,  used  in  polishing  and 
as  a  pigment. 

Kaolin.  A  pure  variety  of  clay,  formed  by  the  decomposition  of  feld- 
spar. 

kelp.  The  ashes  of  seaweeds,  used  as  a  source  of  certain  potash  salts 
and  of  iodine. 

kerosene.  Popularly  called  coal  oil.  An  oil  obtained  by  the  distilla- 
tion of  petroleum. 

kieserite.     Native  magnesium  sulphate. 

kupfer  nickel.     Nickel  arsenide,  NiAs. 

Labarraque's  solution.     Sodium  hypochlorite. 

lac  sulphuris.  Sulphur  precipitated  from  a  solution  of  it  in  lime- 
water. 

laughing  gas.     Nitrous  oxide,  N2O. 

lean  lime.     Lime  made  from  impure  limestone. 

lime.     Calcium  oxide,  CaO. 

limestone.     Calcium  carbonate,  uncrystallized. 

lime-water.     Calcium  hydroxide. 

litharge.     Impure  lead  oxide,  PbO. 

lunar  caustic.     A  commercial  term  for  silver  nitrate. 

Magnesia.     Magnesium  oxide. 

magnesite.     Native  magnesium  carbonate. 

magnetic  pyrites.  A  mixture  of  FeS  and  Fe2S3.  This  mixture  is 
given  its  name  because  of  magnetic  properties. 

malachite.     An  ore  of  copper,  CuCO3,  Cu(OH)2. 

marble.     Crystallized  limestone. 

marcasite.     A  variety  of  ferric  sulphide,  FeS2. 

massicot.    Lead  oxide,  PbO. 


424  MODERN  CHEMISTRY 

milk  of  lime.     Calcium  hydroxide,  containing  more  or  less  lime  in 

suspension. 

milk  of  sulphur.     Same  as  lac  sulphuris. 
minium.     Red  lead,  Pb3O4. 

mispickel.     An  important  ore  of  arsenic,  FeSAs. 
Naphtha.     A  light  oil,  obtained  from  petroleum. 
Nessler's  solution.     A  solution  used  in  testing  for  ammonia, 
niter.     Another  name  for  potassium  nitrate. 
Nordhausen's  acid.     The  same  as  fuming  sulphuric  acid,  H2S207. 
Oil  of  vitriol.     Sulphuric  acid. 
opal.     A  variety  of  silica,  SiO2. 
oriental.     A  term  applied  to  the  true  emerald  and  certain  other  gems,  to 

distinguish  them  from  less  valuable  stones  similar  in  appearance. 
orpiment.     A  sulphide  of  arsenic,  yellow  in  color,  having  composition 


Paraffin.     A  wax  obtained  in  the  later  distillation  of  petroleum. 
Paris  green.     A  popular  name  for  Scheele's  and  Schweinfurth's  green, 

compounds  of  arsenic, 
pearl  ash.     Pure  potassium  carbonate. 
pearl  white.     Bismuth  oxychloride,  BiOCl. 

petroleum.     Rock  oil,  found  native  in  various  parts  of  the  world, 
plaster  of  Paris.     Calcined  calcium  sulphate. 
plastic  sulphur.     A  dark-colored,  allotropic  form  of  sulphur,  somewhat 

resembling  rubber. 
potash.     Another  name  for  commercial  potassium  carbonate.     Also  a 

loose  name  for  potassium  chlorate. 
powder  of  Algaroth.    A  variable  compound  of  antimony,  approximately 

SbOCl. 
purple  of  Cassius.     A  purplish-colored  precipitate  obtained  in  testing 

a  solution  of  gold  with  stannous  chloride. 
pyrites.     A  common  name  for  ferric  sulphide,  FeS2. 
pyrolusite.     Native  manganese  dioxide. 
Quartz.     Silicon  dioxide. 
quicklime.     The  same  as  lime. 
Realgar.     Red  sulphide  of  arsenic,  As2S2. 
red  lead.     The  same  as  minium. 
red  precipitate.     Mercuric  oxide. 

rose  quartz.     A  variety  of  quartz,  somewhat  pink  in  color. 
Sal  ammoniac.     Ammonium  chloride. 


GLOSSARY  425 

sal  soda.     Commercial  sodium  carbonate. 

salt.    A  compound  formed  by  the  union  of  an  acid  and  a  base. 

salt  cake.     Sodium  sulphate. 

saltpeter.     Potassium  nitrate. 

sapphire.     Crystallized  alumina. 

Scheele's  green.     Copper  arsenite,  CuHAsO3. 

silica.     Silicon  dioxide. 

slaked  lime.     Lime  treated  with  water. 

smalt.     A  silicate  of  cobalt  and  potassium. 

smoky  quartz.     A  variety  of  silica,  brown  or  smoky  in  color. 

soda.     Same  as  sal  soda. 

soda,  cooking.     Same  as  sodium  bicarbonate,  NaHC03. 

spathic  iron.     Native  iron  carbonate,  FeCO3. 

specular  iron.     A  variety  of  hematite. 

spiegeleisen.     A  variety  of  iron  containing  manganese  and  carbon. 

stibine.     Same  as  antimoniureted  hydrogen,  SbH3. 

strontianite.     Native  strontium  carbonate. 

subnitrate  of  bismuth.     Basic  bismuth  nitrate,  BiONO3. 

sugar  of  lead.     Lead  acetate. 

Topaz.     Crystallized  alumina  with  small  quantity  of  coloring  matter 

Vermilion.     Artificial  mercuric  sulphide. 

White  arsenic.     Arsenic  trioxide. 

white  lead.    Basic  lead  carbonate,  used  as  a  paint. 

white  vitriol.     Zinc  sulphate. 

witherite.     Native  barium  carbonate. 

Zinc  white.     Zinc  oxide,  ZnO,  used  as  a  paint. 

GLOSSARY  OF  TECHNICAL  TERMS  IN  CHEMISTRY 

Acidify.     To  make  acid. 

acidulate.     To  add  acid  to,  until  no  longer  alkaline  or  neutral. 

actinic.     Referring  to  light  rays,  having  the  power  to  effect  chemical 

changes. 

air-bath.     A  small  oven  used  for  drying  substances, 
alkali.     A  compound  of  hydrogen,  oxygen,  and  some  metallic  element, 

soluble  in  water,  having  the  power  to  neutralize  acids ;  as  caustic 

soda,  NaOH. 
allotropic.     Literally,  another  form;  a  term  applied  to  the  unusual 

form  of  an  element. 


426  MODERN  CHEMISTRY 

allotropism.     The  phenomenon  of  existing  in  two  or  more  forms, 
alloy.     The  product  resulting  from  fusing  together  two  or  more  metals. 
amalgam.     An  alloy,  one  constituent  of  which  is  mercury, 
amorphous.     Without  any  special  form,  uncrystallized,  massive, 
anaesthetic.     An  agent  used  to  produce  insensibility. 
anhydride.     An  oxide,  usually  non-metallic,  which  forms  some  acid 

upon  the  addition  of  water, 
anhydrous.     Without  water.     An  anhydrous  salt  is  one  from  which 

the  water  of  crystallization  has  been  removed, 
anion.     A  negative  ion.     See  ion. 
antiseptic.     A  substance  used  to  prevent  decay,  or  to  destroy  noxious 

germs. 

argentiferous.     Silver-bearing. 
aspirator.     Apparatus  used  to  secure  the  passage  of  air  or  any  other 

gas  through  certain  vessels. 
assay.     Determination  of  the  quantity  of  the  various  constituents  of 

a  metallic  ore. 

Basic.     Having  the  properties  of  an  alkali  or  base, 
binary.     A  compound  consisting  of  two  elements. 
brightening.     The  sudden  brilliant  appearance  of  the  silver  assay  when 

the  lead  has  all  been  removed  by  cupellation. 
bumping.     A  term  applied  to  the  violent  boiling  of  the  liquid  in  a 

vessel,  causing  it  to  jump, 
burette.     A  graduated  tube,  with  stop-cock,  used  in  volumetric  work 

for  measuring  accurately  a  liquid. 
Calcine.     To  heat  strongly. 
carbureting.     Adding  hydrocarbon  compounds  to  an  illuminating  gas, 

as  in  making  water  gas. 
cathion.     An  electropositive  ion. 
cementation.     An  old  process  of  making  steel  by  imbedding  wrought 

iron  in  powdered  charcoal  and  heating  several  days, 
chemism.     The  so-called  affinity  that  one  element  or  substance  has 

for  another. 
commercial.     A  term  applied  to  chemicals  as  usually  furnished  to  the 

trade;  not  absolutely  pure;  in  distinction  from  chemically  pure 

reagents. 

concentrated.     Strong;  undiluted, 
converter.     A  large,  egg-shaped  furnace,  used  in  making  steel  from 

cast  iron  and  in  purifying  copper. 


GLOSSARY  427 

c.  p.    Chemically  pure. 

crucible.  A  small  vessel,  made  to  withstand  great  heat.  Named 
from  the  Latin  word  crux,  because  the  old  alchemists  thus  marked 
their  crucibles. 

crystalline.     Composed  of  crystals. 

cupel.  A  small  cup,  made  of  bone  ashes ;  used  by  assayers  in  deter- 
mining the  gold  and  silver  in  an  ore. 

cupellation.  The  process  of  separating  lead  and  silver  by  the  oxida- 
tion of  the  former. 

Decant.  To  pour  off  the  liquid  from  a  precipitate,  after  the  latter 
has  settled. 

decrepitate.  To  burst  in  pieces  with  a  crackling  sound,  as  many  salts 
do  when  heated  with  the  blowpipe. 

deflagrate.     To  burn  vigorously. 

deflagrating  spoon.  A  small  metallic  cup  or  spoon  with  a  long  wire 
handle  attached.  Used  for  holding  combustible  substances  when 
burning  in  oxygen  or  other  gases. 

deliquesce.     To  take  up  moisture  from  the  air. 

deoxidizing  agent.     See  reducing  agent. 

desiccate.     To  dry. 

desiccator.  A  vessel  used  in  drying  or  keeping  dry  a  substauce  which 
is  to  be  weighed  accurately. 

destructive  distillation.  The  process  of  heating  in  closed  retorts  a 
substance  to  such  a  temperature  as  to  effect  its  decomposition. 

digest.     To  warm  gently. 

disinfectant.  A  substance  used  to  cleanse  and  purify  unwholesome 
places,  as  well  as  to  destroy  disease  germs. 

displacement.  A  method  of  collecting  a  gas  in  a  vessel  filled  with 
air,  or  some  other  gas,  depending  upon  the  difference  in  density 
of  the  two. 

dissociate.     To  break  up  a  compound  body  into  parts. 

distill.     To  evaporate  a  liquid  and  condense  again  in  another  vessel. 

distillate.     The  liquid  obtained  in  the  process  of  distillation. 

dyad.     An  element  having  a  valence  of  two. 

Ebullition.     Rapid  boiling. 

effervescence.  The  act  of  bubbling,  as  seen  upon  the  application  of 
an  acid  to  a  carbonate. 

effloresce.  To  give  up  at  ordinary  temperatures  the  water  of  crystal- 
lization. 


428  MODERN  CHEMISTRY 

electrode.     The  terminal  of  a  battery. 

electro-positive.     A  term  applied  to  elements  attracted  to  the  negative 

electrode. 

equivalence.     A  term  sometimes  used  instead  of  valence, 
escharotic.     An  agent  which  corrodes  or  destroys ;  a  caustic, 
evolve.     To  set  free. 
excess.     A  quantity  more  than  sufficient  to  secure  certain  chemical 

action. 
Filtrate.     The  liquid  obtained  after  passing  through  the  filter  paper, 

in  removing  the  precipitate. 
fixed.     The  opposite  of  volatile. 
flocculent.     Flaky. 
flux.     Any  substance  used  to  lower  the  melting  point  of  another ;  as 

limestone  with  iron  ore  in  the  blast  furnace. 
formula.     A  combination  of  symbols  used  to  represent  a  molecule  of 

a  compound  body. 
fractional  distillation.     The  process  of  separating  by  distillation  the 

several  constituents  of  a  mixture  of  liquids,  by  means  of  their 

different  boiling  points. 

Gangue.     The  impurities  contained  in  an  ore  or  mineral. 
gelatinous.     Like  starch  paste  in  appearance. 
generate.     To  produce  or  set  free,  as  a  gas. 
germicide.     A  substance  used  to  destroy  bacteria  or  germs. 
granulated.     In  irregularly  shaped  small  particles,  secured  by  pouring 

the  fused  metal  into  cold  water. 
graphitoidal.     Resembling  graphite. 
gravimetric.     Measurement  or  estimation  by  weight. 
Halogen.     Literally,   salt  producer;    applied  to  the  members  of  the 

chlorine  group. 
hydrated.     Containing  water, 
hydroxyl.     A  term  applied  to  the  radical  OH. 
hygroscopic.     Applied  to  substances  which  readily  absorb  moisture 

from  the  air. 
Ignite.     To  set  fire  to. 
indicator.     A  substance  used  to  show  the  completion  of  a  chemical 

reaction. 

inflammable.     Combustible, 
ion.     An  atom  or  group  of  atoms  in  a  solution,  which  serves  as  a 

carrier  of  electricity. 


GLOSSAET  429 

ionization.     The  separation  of  a  substance  into  ions. 

isomeric.  Applied  to  substances  having  the  same  percentage  composi- 
tion, though  differing  in  characteristics. 

isomorphous.     Of  the  same  crystalline  form. 

Leach.  To  treat  with  water;  to  remove  the  soluble  salts  from  a 
mixture  of  substances  by  means  of  water. 

liquation.  The  process  of  separating  one  metal  from  another  by 
cautiously  fusing,  so  that  one  will  flow  out  before  the  melting 
point  of  the  other  is  reached. 

lixiviate.     Synonymous  with  leach. 

lute.     To  seal  air-tight. 

Manipulation.     Setting  up  or  arranging  apparatus  for  experiment. 

matte.  A  mixture  of  metallic  sulphides  obtained  in  the  early 
stages  of  the  reduction  of  copper  ores,  containing  lead,  silver, 
etc. 

meniscus.  The  upper  curved  surface  of  a  liquid  contained  in  a  small 
tube. 

monad.     An  element  the  valence  of  which  is  one. 

mono-basic.  A  term  applied  to  an  acid  having  only  one  replaceable 
atom  of  hydrogen. 

mordant.     A  substance  used  to  set  the  color  in  dyeing. 

mother  liquor.  The  liquid  remaining  after  the  principal  salt  con- 
tained in  solution  has  been  removed  by  crystallization. 

Nascent.  Applied  to  a  gas  when  first  liberated  from  its  compound. 
It  is  believed  to  exist  then  in  the  atomic  condition. 

native.     Not  in  combination,  free. 

neutral.     Neither  acid  nor  alkaline. 

neutralization.  The  combination  of  an  acid  with  an  alkali  so  as  to 
destroy  the  properties  of  each,  and  produce  a  salt. 

nitrogenous.  Containing  nitrogen.  Organic  matter  containing  nitro- 
gen is  thus  characterized. 

Occlude.  To  condense  upon  the  surface  or  within  the  pores.  Especially 
seen  in  the  action  of  platinum  upon  hydrogen. 

oxidation.     The  union  of  a  substance  with  oxygen. 

oxidizing  agent.  A  substance  which  readily  gives  up  a  portion  of  its 
oxygen  to  combine  with  some  other  substance. 

oxygenized.     Containing  considerable  oxygen. 

Paste.  A  special  variety  of  glass,  used  sometimes  for  making  imita- 
tion diamonds. 


430  MODERN  CHEMISTRY 

pigs.     The  term  applied  to  cast  iron  as  molded  when  first  drawn  from 

the  blast  furnace.    Applied  also  to  the  molds  themselves. 
pipette.     A  small  graduated  glass  tube   used  in  measuring  small 

quantities  of  a  liquid. 
pneumatic.     Pertaining  to  gases ;  applied  to  the  trough  or  pan  used 

in  collecting  gases. 
polymerism.     A  term  referring  to  the   cases  of  compounds  which 

have  the  same  percentage  composition,  but  different  molecular 

weights. 

precipitate.     A  solid  thrown  down  in  a  liquid  by  some  reagent. 
Qualitative  analysis.     The  determination  of  the  kind  of  matter  which 

enters  into  a  substance. 

quantitative  analysis.     The  determination  of  the  amount  of  a  sub- 
stance contained  in  a  compound. 

Radical.  A  group  of  atoms  which  seems  to  act  as  a  single  atom, 
reaction.  The  action  of  two  or  more  substances  upon  each  other, 
reagent.  A  substance  used  to  bring  about  some  chemical  change, 
reducing  agent.  A  substance  used  to  convert  a  compound  from  a 

higher  to  a  lower  order,  as  from  an  ic  to  an  ous  compound ;  or, 

to  remove  the  oxygen  from  an  oxide, 
residual.     That  which  remains, 
reverberatory.     A  variety  of  furnace,  usually  of  low,  arching  ceiling. 

See  Fig.  57  in  text. 
roast.     To  heat  strongly;   to  oxidize  metallic  ores,   expelling  the 

sulphur  as  SO2. 
Sand-bath.     A  small  iron  saucer  containing  sand,  used  the  same  as  a 

wire  screen  in  protecting  glassware  when  being  heated, 
saturated.     Fully  satisfied;  containing  all  it  can  hold, 
scintillate.     To  burn  with  sparks. 
siliceous  earth.     Material  consisting  largely  of  silica, 
slag.     The  dark-colored  glass  formed  in  the  reduction  of  metallic  ores 

from  the  flux  used  and  the  gangue  present. 
solvent.     A  liquid  which  dissolves  some  particular  substance, 
spit.     Silver  on   being  melted   absorbs  considerable  oxygen.     Upon 

cooling  it  again  expels  this,  sometimes  with  considerable  energy, 

throwing  out  fine  particles  of  the  molten  silver.     This  is  termed 

spitting. 

stable.     Not  easily  decomposed, 
sublimate.     The  substance  obtained  by  sublimation. 


GLOSSARY  431 

sublimation.  The  vaporizing  of  a  solid  and  recondensing.  The  same 
in  reference  to  solids  that  distillation  is  with  liquids. 

supernatant.  Said  of  a  liquid  overlying  a  precipitate  after  the  latter 
has  subsided. 

suspension.  Said  of  a  solid  in  the  form  of  fine  particles  floating 
throughout  the  liquid. 

symbol.     A  letter  or  letters  representing  an  atom  of  an  element. 

Thio.     From  a  Greek  word,  meaning  sulphur. 

treat.     To  apply  or  add  to. 

triad.     An  element  having  a  valence  of  three. 

tubulated.  Applied  to  a  flask  having  a  small  tube-like  opening  in  the 
side,  fitted  with  a  stop-cock. 

tubulure.     A  small,  tube-like  opening. 

tuydre.  A  blast  or  air  pipe  for  conducting  the  strong  currents  of  air 
into  the  blast  furnace. 

Valence.  The  power  which  an  atom  or  group  of  elements  has  of  com- 
bining with  some  other  element  taken  as  a  standard. 

volatile.     Easy  to  vaporize. 

volatilize.     To  drive  off  in  the  form  of  vapor. 

volumetric.    Estimation  of  the  quantity  of  a  substance  ti& Jhfeasuring. 


INDEX 


Absolute  thermometer,  95. 
Absolute  zero,  95. 
Acetic  acid,  test  for,  345. 
Acetylene,  burners  for,  150. 

characteristics  of,  150. 

experiments  with,  151,  152. 

generators,  149. 

preparation  of,  148. 
Acids,  125. 

classes  of,  343. 

composition  of,  126. 

detection  of,  343. 

nomenclature  of,  128. 

preliminaries  to  testing,  345,  347. 

properties  of,  125. 

Air,  estimation  of  its  constituents, 
350. 

estimation  of  weight,  97. 

liquefaction  of,  97. 
Air-slaked  lime,  222. 
Alchemistic  terms,  386. 
Alkali  earths,  219. 
Alkalies,  125. 
Alkali  metals,  207. 
Allotropism,  59. 
Aluminum,  263. 

bronze,  235. 

characteristics  of,  264. 

hydroxide,  269. 

source  of  supply,  263. 

test  for,  337. 

uses,  264. 
Alums,  266. 

kinds  of,  267. 

preparation  of,  266. 

uses  of,  267. 

uses  of,  for  clarifying  water,  268. 


Amalgams,  258. 

methods  of  making,  258. 
Ammonia,  73. 

absorption  of,  by  charcoal,  78. 

as  a  refrigerant,  78. 

characteristics  of,  76. 

commercial  supply,  74. 

decomposition  of,  by  platinum,  78. 

estimation  of  the  constituents,  351. 

fountain,  77. 

preparation  for  commerce,  74. 

test  for,  342. 

uses,  78. 

Ammonium,  67. 
Anhydride,  83. 
Anions,  329. 
Antichlor,  112. 

Antimoniureted  hydrogen,  292. 
Antimony,  290. 

amorphous,  292. 

black,  292. 

characteristics  of,  291. 

chloride,  293. 

oxides,  293. 

oxy chloride,  293. 

reduction  of  ore,  290. 

sulphide,  294. 

test  for,  334. 

uses,  292. 

Apparatus  for  pupils,  357. 
Aqua  regia,  88. 
Argentite,  238. 
Argon,  characteristics  of,  90. 

discovery,  89. 

Arrangement  of  bottles,  356. 
Arsenic,  characteristics  of,  286. 

Marsh's  test  for,  287. 


434 


INDEX 


oxides,  288. 

reduction  of  ores,  285. 

source  of  supply,  285. 

sulphide,  290. 

uses  of,  286. 
Arsenical  pyrite,  285. 
Arsine,  287. 
Asbestos,  219. 
Aspirators,  370. 
Atmosphere,  91. 
Atom,  definition  of,  11. 
Atomic  weights,  68. 

determination  of,  198. 
Avogadro's  Law,  190. 

application  of,  198. 

proof  of,  196. 
Azurite,  233. 

Banca  tin,  270. 
Barium,  229. 

carbonate,  229. 

chloride,  229. 

hydroxide,  230. 

nitrate,  229. 

separation  from  calcium,  340. 

sulphate,  229. 

tests  for,  340. 
Barometric  reading,  correction  of, 

374. 

Baryta,  229. 
Base,  124. 
Bauxite,  264. 
Bell  metal,  235. 
Bessemer  steel,  303. 
Binary  compounds,  131. 
Biographical  appendix,  382. 
Bismuth,  294. 

characteristics  of,  294. 

compounds,  classes  of,  295. 

nitrate,  295. 

ocher,  296. 

oxychloride,  296. 

trichloride,  296. 

trioxide,  296. 

uses,  295. 


Bismuthite,  294. 

Bismuthyl  compounds,  295. 

Black  ash,  211. 

Black  lead,  136. 

Blast  furnace,  300. 

Bleaching  powder,  227 

Bloom,  302. 

Blowpipe  work,  361. 

Blue  prints,  245. 

Blue  vitriol,  235. 

Bohemian  glass,  188. 

Bordeaux  mixture,  236, 

Bornite,  233. 

Bottles,  opening  of,  366. 

Boyle's  Law,  93. 

Brass,  235. 

Bromides,  test  for,  344. 

Bromine,  characteristics  of,  117. 

commercial  supply,  116. 

experiments  with,  118. 

occurrence  of,  116. 

preparation  of,  117. 

test  for,  117. 

uses,  118. 
Bronze,  235. 
Burnt  alum,  267. 

Cadmium,  254. 

characteristics  of,  255. 

nitrate,  256. 

reduction  of,  255. 

sulphide,  256. 

test  for,  334. 
Calchopyrite,  233. 
Calcite,  221. 
Calcium,  220. 

carbide,  148. 

carbonate,  223. 

characteristics  of,  221. 

chloride,  224. 

history  of,  221. 

hydroxide,  223. 

oxide,  221. 

sulphate,  224. 
Calomel,  260. 


INDEX 


435 


Carbon,  abundance  of,  135. 

as  an  absorbent,  139. 

as  a  reducing  agent,  139. 

forms  of,  135. 

uses  of,  140. 
Carbon  dioxide,  142. 

characteristics  of,  144. 

estimation  of,  348. 

liquid,  144. 

preparation  of,  143. 

source  of,  142. 

uses  of,  144. 
Carbon  monoxide,  141. 
Carre's  ice  machine,  79. 
Cassiterite,  270. 
Cast  iron,  302. 

Castner's  process  for  sodium,  208. 
Catalysis,  51. 
Cathions,  329. 
Caustic  soda,  209. 
Cements,  225. 

composition  of,  226. 
Chamber  acid,  181. 
Charcoal,  137. 
Charles's  Law,  94. 

problems  with,  96. 
Chemical  changes,  15. 

experiments  to  illustrate,  15,  1C, 

17,  18. 

Chloric  acid,  345. 
Chlorine,  as  a  bleaching  agent,  111. 

characteristics  of,  109. 

chemistry  of  its  preparation,  106. 

Deacon's  process,  106. 

experiments  with,  108. 

history  of,  102. 

liquid,  110. 

occurrence,  103. 

preparation,  103. 

uses  of,  111. 

water,  105. 

Weldon's  process,  104. 
Choke  damp,  144. 
Chromic  acid,  321. 
Chromium,  317. 


compounds,  317. 

conversion  of  compounds,  319. 

hydroxide,  321. 

oxides,  320. 

test  for,  337. 

uses  of,  321. 
Chromite,  317. 
Cinnabar,  257,  260. 
Clay,  265. 
Coal,  137. 
Coal  gas,  153. 
Cobalt,  311. 

compounds,  311. 

test  for,  338. 
Coke,  138. 

Combination,  laws  of,  166. 
Combining  weights,  164. 
Combustible  substances,  57C 
Combustion,  56. 
Compounds,  10. 

saturated,  24. 
Converter,  303. 
Copper,  232. 

alloys  of,  235. 

blister,  233. 

characteristics  of,  234. 

pyrite,  233. 

reduction  of,  233. 

salts,  235. 

supply  of,  232. 

tests  for,  233. 
Copperas,  308. 
Corals,  221. 

Corrosive  sublimate,  260. 
Corundum,  265. 
Crocosite,  317. 
Crown  glass,  188. 
Cryolite,  264. 
Cupel,  239. 
Cupellation,  239. 
Cupola  furnace,  304. 
Cupric  acetylide,  236. 

chloride,  236. 

nitrate,  236. 

oxide,  237. 


430 


INDEX 


sulphate,  235. 
sulphide,  286. 
Cyanide  process  for  gold,  247. 

Decanting,  364. 

Definite  Proportions,  Law  of,  158. 

Deliquescent  bodies,  31. 

Delivery  tubes,  preparation  of,  358. 

Dewar  bulbs,  97. 

Diamonds,  135. 

practical  uses,  136. 
Diatomic  molecules,  200. 
Diffusion  of  gases,  92. 
Dissociation,  329. 
Distillation,  destructive,  137. 

fractional,  137. 
Dolomite,  219. 

Downward  displacement,  362. 
Drying  of  tubes,  375. 
Dyads,  23. 
Dynamite,  89. 

Efflorescent  bodies,  30. 
Electrolysis  of  water,  32. 
Electrolytic  apparatus,  367. 
Elements,  classes  of,  204. 

definition  of,  8. 

table  of,  8,  204,  388. 

vacancies  in  table,  206. 

valence  of,  8. 
Emerald,  265. 
Emery,  265. 
Epsom  salts,  220. 
Equations,  27. 

exercise  in,  28. 

writing,  69. 

value  of,  69. 
Etching  glass,  102. 
Ethylene,  147 
Euchlorine,  105. 
Eudiometer,  33,  369. 
Experiments,  recording,  376. 

Feldspar,  265. 
Ferric  chloride,  308. 


oxide,  309. 

salts,  how  changed  to  ferrous,  307< 

salts,  how  distinguished,  306. 

sulphate,  308. 

sulphide,  308. 

Ferrous  salts,  how  changed  to  ferric, 
307. 

how  tested,  306. 
Fertilizers,  194. 
Filter  flask,  370. 
Filtering,  364. 
Fire  damp,  146. 
Fixing  bath,  244. 
Flame,  58. 

Flame  tests  tor  barium,  etc.,  230. 
Flint  glass,  188. 
Fluorine,  101. 

compounds  of,  102. 
Fool's  gold,  300. 
Formulae,  determination  of,  201. 

meaning  of,  66. 
Franklinite,  250. 

Galena,  274. 
Ganister,  303. 
Gas  carbon,  138. 
Gas  generators,  373. 
Gases,  collecting,  362. 

illuminating,  152. 
German  silver,  253. 
Glacial  phosphoric  acid,  194. 
Glass,  187. 

annealing,  189. 

cutting,  358. 

etching,  102. 

manufacture  of,  187. 

varieties  of,  188. 
Glauber's  salt,  212. 
Glossary   of  chemicals   and   min- 
erals, 391. 

Glossary  of  technical  terms,  396. 
Gold,  246. 

characteristics  of,  248. 

methods  of  mining,  246. 
Graphite,  136. 


WDEX 


437 


Greek  fire,  175. 
Green  fire,  229. 
Greenockite,  255. 
Green  vitriol,  308. 
Guncotton,  89. 
Gunpowder,  175. 

separation  of,  19. 
Gypsum,  221. 

Halogens,  101. 

comparison  of,  122. 
Hard  waters,  226. 
Harveyized  steel,  310. 
Heavy  spar,  229. 
Hematite,  299. 
Horn  silver,  238. 
Hydraulic  cement,  225. 
Hydraulic  mining,  246. 
Hydriodic  acid,  test,  344. 
Hydrobromic  acid,  test,  344. 
Hydrocarbons,  146. 
Hydrochloric  acid,   characteristics 
of,  115. 

commercial  supply,  113. 

composition  of,  proof,  354. 

composition  of,  estimation,  352. 

experiments  with,  114. 

history  of,  112. 

preparation  of,  112. 

test  for,  344. 

uses,  115. 
Hydrogen,  36. 

characteristics  of,  42. 

experiments  with,  42. 

liquid,  45. 

methods  of  preparing,  36. 

occlusion  of,  44,  314. 

uses,  45. 

Hydrogen  dioxide,  63. 
Hydrogen  sulphide,  175. 
Hydroxides,  125. 
Hydroxyl,  66. 

Iceland  spar,  221. 
Ice  machine,  78,  80. 


Ice  manufacture,  79. 
Illuminating  gases,  152. 

composition  of,  155. 

manufacture  of,  153. 
Iodides,  test  for,  344. 
Iodine,  119. 

characteristics  of,  121. 

experiments  with,  121. 

preparation  of,  119. 

solvents  for,  122. 

uses,  122. 
Ionic  theory,  328. 
lonization,  329. 
Ions,  329. 
Iridium,  314. 
Iron,  cast,  302. 

compounds  of,  305. 

distribution  of,  299. 

forms  of,  305. 

protoxide,  309. 

pyrite,  300. 

reduction  of,  302. 

test  for,  337. 

uses,  305. 

wrought,  302. 

Jets,  preparation  of,  359. 

Kaolin,  265. 

Kindling  temperature,  57. 

Laboratory  suggestions,  355. 
Lampblack,  139. 
Lead,  274. 

acetate,  279. 

carbonate,  280. 

characteristics  of,  277. 

chloride,  279. 

chromate,  282. 

nitrate,  279. 

oxides,  280. 

reduction  of  ores,  275. 

sulphate,  279. 

sulphide,  282. 

tests  for,  283,  331. 

uses,  277. 


438 


INDEX 


Leblanc's  process  for  soda,  211. 
Lime,  221. 

properties  of,  222. 
Limonite,  300. 
Linde's  apparatus,  98. 
Liquid  air,  100. 

apparatus  for,  98. 
Liter,  weight  of,  201. 
Litharge,  280. 
Lithium,  test  for,  342. 
Lunar  caustic,  243. 

Magnesia,  220. 
Magnesium,  219. 

compounds,  220. 

test  for,  340. 
Magnetite,  299. 
Malachite,  233. 
Manganese,  323. 

compounds  of,  323. 

dioxide,  324. 

dioxide,    as    a    catalytic    agent, 
50. 

test  for,  338. 
Manganic  acid,  324. 
Marsh  gas,  146. 
Marsh's  test  for  arsenic,  287. 
Matte,  233. 
Matter,  11. 

theories  of,  8. 
Measurements,  363. 
Meerschaum,  219. 
Mercuric  chloride,  260. 

nitrate,  259. 

oxide,  260. 

salts,  distinguished,  261. 

sulphide,  260. 
Mercurous  chloride,  260. 

nitrate,  259. 
Mercury,  256. 

characteristics  of,  257. 

reduction  of,  257. 

solvents  for,  259. 

tests  for,  331,  333. 

uses,  259. 


1  Metals,  203. 

displacing  power  of,  169. 
Metaphosphoric  acid,  194. 
Meteorites,  299. 
Methane,  146. 
Micro-crith,  68. 
Minium,  280. 
Mixtures,  18. 
Molecular  weight,  68. 
Molecules,  11. 

constitution  of,  199. 

of  compound  bodies,  12. 
Monads,  23. 

Monatomic  molecules,  200. 
Monobasic  acids,  194. 
Mortar,  222. 

Multiple     Proportions,    Law 
161. 

Natural  gas,  155. 
Negatives,  photographic,  244. 
Neutralization,  124. 
Nickel,  309. 

compounds  of,  310. 

tests  for,  311,  338. 

uses,  310. 
Nitric  acid,  characteristics  of,  87. 

in  the  air,  86. 

preparation  of,  86. 

test  for,  85. 

uses,  88. 
Nitric  oxide,  82. 

characteristics  of,  83. 
Nitrogen,  71. 

characteristics  of,  73. 

oxides  of,  81. 

pentoxide,  86. 

tetroxide,  85. 

uses  of,  73. 
Nitrogen  group,  297. 
Nitroglycerine,  89. 
Nitrous  acid,  preparation,  84. 

test  for,  84. 
Nitrous  anhydride,  83. 

oxide,  81, 


INDEX 


439 


Occlusion,  44,  314. 
Oil  of  vitriol,  179. 
Olefiant  gas,  147. 
Orpiment,  285. 
Osmium,  314. 
Oxidation,  56. 
Oxides,  132. 
Oxidizing  flame,  361. 
Oxygen,  47. 

characteristics  of,  54. 

determination  of  weight,  55. 

experiments  with,  49. 

liquid,  54. 

Motay's  method,  52. 

preparation,  48. 

preparation  from  potassium  per- 
manganate, 53. 

uses,  55. 

Oxy-hydrogen  blowpipe,  58. 
Ozone,  59. 

characteristics  of,  61. 

comparison  with  oxygen,  60. 

liquid,  61. 

Palladium,  314. 

Panning  gold,  246. 

Paris  green,  289. 

Parke's  method,  239. 

Paste,  188. 

Pattison's  method,  239. 

Pearl  ash,  216. 

Pearl  white,  297. 

Pentads,  23. 

Periodic  Law,  204. 

Phosphates,  194. 

Phosphine,  192. 

Phosphoric  acid,  test  for,  344. 

Phosphorus,  190. 

acids  of,  194. 

characteristics  of,  191. 

manufacture  of,  190. 

oxides  of,  193. 

uses  of,  192. 
Photographic  papers,  244. 

plates,  243. 


Photography,  243. 
Physical  changes,  12. 

illustration  of,  13. 

experiments,  12,  14. 
Pig  iron,  302. 
Pintsch  gas,  154. 
Placer  mining,  246. 
Plaster  of  Paris,  224. 
Platinum,  314. 

alloys  of,  315. 

spongy,  314. 

uses,  316. 

wires,  366. 
Polymerism,  62. ' 
Porcelain,  265. 
Potassium,  214. 

bromide,  217. 

carbonate,  216. 

chlorate,  216. 

chromate,  318. 

dichromate,  318. 

hydroxide,  215. 

iodide,  217. 

nitrate,  217. 

permanganate,  324,  325. ' 

tests  for,  217,  342. 
Precipitates,  364. 
Prefixes,  per,  pro,  etc.,  133. 
Pressure,  standard,  93. 
Puddling  furnace,  302. 
Pyrite,  300. 
Pyrolusite,  323. 

Qualitative  analysis,  327. 
Quantitative   experiments,  carbon 

dioxide,  estimation  of,  348. 
combining     weight     of     copper, 

164. 

combining  weight  of  tin,  165. 
composition  of  air,  350. 
composition  of  ammonia,  351. 
composition  of  hydrochloric  acid, 

352. 

definite  proportions,  proof  of  law, 
158,  159,  160,  161. 


440 


INDEX 


displacing      power,      aluminum, 
170. 

magnesium,  171. 
zinc,  170. 

electrolysis  of  water,  32. 

manganese  dioxide  as  a  catalytic 
agent,  proof  of,  51. 

multiple    proportions,    proof    of 
law,  162. 

strength  of  acid,  determination  of, 
167. 

strength  of  alkali,  determination 
of,  167. 

strength  of  salt  solution,  determi- 
nation of,  169. 

synthesis  of  water,  33,  34. 

water  of  crystallization,  determi- 
nation of,  349. 

weight  of  1  liter  of  air,  97. 

weight  of  1  liter  of  oxygen,  55. 
Quicksilver,  256. 

Radicals,  66. 
Reactions,  67. 
Realgar,  285. 
Red  fire,  228. 
Red  precipitate,  260. 
Reducing  flame,  361. 
Reference  library,  381. 
Rose  quartz,  186. 
Ruby,  265. 

Safety  lamp,  147. 
Saltpeter,  217. 

Chile,  212. 
Salts,  acid,  127. 

definition  of,  127. 

formulae  of,  128. 

nomenclature  of,  130. 

normal,  127. 
Sapphire,  265. 
Scheele's  green,  289. 
Scheele's  test  for  arsenic,  290. 
Separation  of  metals,  arsenic,  an- 
timony, tin,  334. 


barium,  strontium,  calcium,  mag- 
nesium, 340. 

bismuth,  copper,  cadmium,  333. 

iron,  chromium,  aluminum,  337. 

lead,  silver,  mercury,  330. 

nickel,  cobalt,  manganese,  zinc,  338 

sodium,  potassium,  lithium,  342. 
Shot,  278. 
Siderite,  300. 
Silica,  186. 
Silicates,  186. 
Silicic  acid,  187. 
Silicon,  184. 
Silver,  238. 

characteristics  of,  241. 

chloride,  242. 

chromate,  242. 

experiments  with,  240. 

nitrate,  241. 

Parke's  process,  239. 

Pattison's  process,  239. 

reduction  of  ores,  238. 

test  for,  332. 

uses,  241. 
Smalt,  312. 
Smithsonite,  250. 
Smoky  quartz,  186. 
Soap,  212. 

hard  and  soft,  213. 
Sodium,  207. 

carbonate,  210. 

characteristics  of,  208. 

chloride,  209. 

effects  upon  water,  38. 

experiments  with,  38. 

hydroxide,  209. 

nitrate,  212. 

preparation  of,  210. 

sulphate,  212. 

tests  for,  214,  342. 
Sodors,  145. 
Solder,  278. 
Solubility  of  salts,  346. 
Solutions,  preparation  of,  376. 
Solvay  process  for  soda,  210. 


INDEX 


441 


Sparklets,  145. 
Spathic  iron,  300. 
Spelter,  253. 
Spiegeleisen,  304. 
Stalactite,  231. 
Stannic  chloride,  272. 

oxide,  274. 

sulphide,  273. 
Stannous  chloride,  272. 

sulphide,  273. 
Steel,  303. 

basic  lining  process,  304. 

comparison  with  cast  iron,  305. 

tempering,  305. 
Stibine,  292. 
Stibnite,  290. 
Strass,  188. 
Strontianite,  228. 
Strontium,  228. 

carbonate,  228. 

hydroxide,  229. 

nitrate,  228. 

separation  of,  340. 

tests  for,  340. 
Sugar  of  lead,  279. 
Suint,  214. 

Sulphides,  test  for,  304. 
Sulphur,  171. 

acids  of,  179. 

allotropic,  174. 

characteristics  of,  173. 

forms  of,  174. 

oxides  of,  177. 

source  of  supply,  172. 

uses,  175. 
Sulphur  dioxide,  177. 

characteristics  of,  178. 

uses,  179. 
Sulphuric  acid,  179. 

characteristics  of,  182. 

manufacture  of,  181. 

test  for,  181,  343. 

uses,  183. 
Sulphurous  acid,  183. 

test  for,  344. 


Supplies  needed,  378. 
Supporters  of  combustion,  57. 
Symbols,  65. 
Sympathetic  inks,  312. 
Synthesis  of  water,  33. 

Tables  : 

comparison  of  oxygen  and  ozone, 
62. 

comparison  of  metals  and  non- 
metals,  203. 

composition  of  cements,  226. 

compounds  of  chromium,  318. 

compounds  of  manganese,  326. 

iron  salts, distinctions  between,306. 

names  of  elements,  9,  388. 

nitrogen  group,  297. 

periodic  law,  204. 

salts  of  mercury,  261. 

separation  of  metals, 

group  I,  331. 
group  II,  336. 
group  III,  339. 
group  IV,  341. 
group  V,  343. 

tension  of  aqueous  vapor,  374. 

three  forms  of  iron,  305. 

valence,  27. 

Ternary  compounds,  131. 
Test-tube  repairing,  360. 
Tetrads,  23. 
Thiosulphuric  acid,  184. 

test  for,  344. 
Tin,  270. 

alloys  of,  272. 

characteristics  of,  270. 

foil,  272. 

plate,  272. 

salts,  272. 

stone,  270. 

test  for,  335. 

uses,  272. 
Triads,  23. 
Tribasic,  194. 
Type-metal,  278. 


442 


INDEX 


Univalent  atoms,  23. 
Upward  displacement,  362. 

Valence,  definition  of,  21. 

double,  25. 

exercise  in,  26. 

illustration  of,  22. 

of  radicals,  25. 

variation  of,  23. 
Vapor  density,   determination    of, 

200. 

Vein  mining  for  gold,  246. 
Vermilion,  260. 
Vitriol,  oil  of,  179. 

blue,  335. 

green,  308. 

white,  253. 

Wash  bottle,  preparation  of,  359. 
Water,  abundance  of,  29. 

analysis  of,  32,  34. 

characteristics  of,  31. 

composition  of,  32. 

decomposition  by  sodium,  37. 

forms  of,  29. 

solvent  powers  of,  32. 

synthesis  of,  33. 
Water  gas,  154. 
Water  glass,  187. 


Water  of  crystallization,  30. 

estimation  of,  349. 

proof  of,  30. 
Weldon's  mud,  105. 
White  arsenic,  288. 
White  lead,  280. 

Dutch  method  of  preparation,  280 

electrolytic  method,  281. 

Milner's  method,  281. 
White  vitriol,  253. 
Witherite,  229. 
Wrought  iron,  302. 

Zinc,  250. 
alloys  of,  253. 
blende,  250. 
characteristics  of,  252. 
chloride,  253. 
hydroxide,  254. 
ores,  250. 
oxide,  254. 

reaction  with  acids,  40. 
reduction  of,  250. 
sulphate,  253. 
sulphide,  254. 
test  for,  338. 
uses,  253. 
white,  254. 


If 


I1 


Millimetres  X  .03937  =  inches. 
Millimetres  -*-  25.4  =  inches. 
Centimetres  X  .3937  =  inches. 
Centimetres  -4-  2.54  =  inches. 
Metres  X  39.37  =  inches.  (Act  Congress.) 
Metres  X  3.281  =  feet. 
Metres  X  1.094  =  yards. 
Kilometres  X  .621  =  miles. 
Kilometres  -4-  1.6033  =  miles. 
Kilometres  X  3280.8693  =  feet. 
Square  Millimetres  X  .00155  =  sq.  inches. 
Square  Millimetres -5- 645.1  =  sq.  inches. 
Square  Centimetres  X  .155  =  sq.  inches. 
Square  Centimetres  H-  6.451  =  sq.  inches. 
Square  Metres  X  10.764  =  sq.  feet. 
Square  Kilometres  X  247.1  =  acres. 
Hectare  X  2.471  =  acres. 
Cubic  Centimetres  -i-  16  383  =  cubic  inches. 
Cubic  Centimetres  -*-3. 6U  =  fl.  drams  (U.S.P.) 
Cubic  Centimetres-^-29.57=fluid  oz.  (U.S.P.) 
Cubic  Metres  X  35.315  =  cubic  feet. 
Cubic  Metres  X  1-308  =  cubic  yards. 
Cubic  Metres  X  264.2  =  gallons  (231.  cu.  in.) 
Litres  X  61.022  =  cubic  in.  (Act  Congress.) 
Litres  X  33.84  =  fluid  ounces  (u.  s.  PHAK.) 
Litres  X  .2642  =  gallons  (231.  cu.  in.) 
Litres  -*-  3.78  =  gallons  (231.  cu.  in.) 


Litres  -j-  28.31(5  =  cubic  feet. 
Hectolitres  X  3.531  =  cubic  feet. 
Hectolitres  X  2.84  =  bushels  (2150.42  cu.in.) 
Hectolitres  X  .131  =  cubic  yards. 
Hectolitres  -^  2C.42  =  gallons  (231.  cu.  in.) 
Grammes  X  15.432  =  grains.  (Act  Congress) 
Grammes  -s-  981.=  dynes. 
Grammes  (water)  H-  29.57  =  fluid  ounces. 
Grammes  -s-  23.35  =  ounces  avoirdupois. 
Grammes  per  cu.  cent.-s-27.7=lbs.  per  cu.  inu 
Joule  X  .7373  =  foot  pounds. 
Kilo-gramines  X  2.2046  =  pounds. 
Kilo-gramines  X  35.3  =  ounces avoirdupofs. 
Kilo-grammes  -f-  907.2  =  tons  (2,000  Ibs.) 
Kilo-gr.  per  sq. cent.  X 14  223= Ibs.  per  sq.  in. 
Kilo-gram-metres  X  7.233  =  foot  Ibs. 
Kilo-gr.  per  Metre  X  .672  =  Ibs.  per  foot. 
Kilo-gr.  per  Cu.  Metre  X  .062  =  Ibs.  per  cu.  ft. 
Tonneau  X  1.1023  =  tons  (2,000  Ibs.) 
Kilo-Watts  X  1.34  =  Horse  Power. 
Watts  -*-  746.  =  Horse  Power. 
Watts  X  .7373  =  foot  pounds  per  second. 
Calorie  X  3.968  =  B.  T.  U. 
Cheval  vapeur  -*-  .9863  =  Horse  Power. 
(Centigrade  X  1.8)-f32=degree  Fahrenheit. 
Franc  X  .193  =  Dollars. 
Gravity  Paris=980.94  centimetres  per  sec. 


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